RECORD: Darwin, C. R. 1854. A monograph on the sub-class Cirripedia, with figures of all the species. The Balanidæ, (or sessile cirripedes); the Verrucidæ, etc. etc. etc. London: The Ray Society. Volume 2

REVISION HISTORY: Transcribed for John van Wyhe 2002. Further corrections John van Wyhe 2003. Corrected by Sue Asscher 11.2006. Scanned by van Wyhe 2005, spine scanned by Angus Carroll 5.2008. RN2

NOTE: See Marsha Richmond's introduction Darwin's Study of the Cirripedia.

See bibliographical introduction by R. B. Freeman.

The copy scanned was kindly provided by Richard Darwin Keynes. The spine image is from a copy in the collection of Angus Carroll.


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THE

RAY SOCIETY.

INSTITUTED MDCCXLIV.

LONDON.

MDCCCLIV.

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A MONOGRAPH

ON THE SUB-CLASS

CIRRIPEDIA,

WITH

FIGURES OF ALL THE SPECIES.

BY

CHARLES DARWIN, F.R.S., F.G.S.

————

THE BALANIDÆ,

(OR SESSILE CIRRIPEDES);

THE VERRUCIDÆ,

ETC., ETC., ETC.

————

LONDON:

PRINTED FOR THE RAY SOCIETY.

MDCCCLIV.

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————————————————————

J. E. ADLARD, PRINTER, BARTHOLOMEW CLOSE.

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TO

PROFESSOR H. MILNE EDWARDS,

DEAN OF THE FACULTY OF SCIENCES OF PARIS; PROFESSOR AT THE MUSEUM OF NATURAL HISTORY; MEMBER OF THE INSTITUTE OF FRANCE;
FOREIGN MEMBER OF THE ROYAL SOCIETY OF LONDON, OF THE ACADEMIES OF BERLIN, STOCKHOLM, ST. PETERSBURG, VIENNA, KONIGSBERG, MOSCOW, BRUSSELS, HAARLEM, BOSTON, PHILADELPHIA, ETC.

THIS WORK IS DEDICATED,

WITH THE MOST SINCERE RESPECT,

AS THE ONLY, THOUGH VERY INADEQUATE ACKNOWLEDGMENT
WHICH THE AUTHOR CAN MAKE OF HIS GREAT AND
CONTINUED OBLIGATIONS TO THE

'HISTOIRE NATURELLE DES CRUSTACÉS,'

AND TO

THE OTHER MEMOIRS AND WORKS ON NATURAL HISTORY PUBLISHED BY

THIS ILLUSTRIOUS NATURALIST.

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PREFACE.

HAVING so lately, in my volumes on the Recent and Fossil Lepadidæ, expressed as strongly as I could, and with the utmost sincerity, the obligations under which I lie to very many naturalists, I will not here repeat my thanks, and will only say that the assistance formerly rendered me from so many quarters has been most kindly continued without intermission. The references under the Habitats, in which I may remark the names of Mr. Cuming and of Mr. Stutchbury, and of the British Museum, so often recur, show my deep obligations to these gentlemen and to Dr. Gray, and indeed to most of the British and several Foreign* collectors of recent and fossil shells. At the period when the Introduction to this volume was printed, I stated that I did not know whether the Palæontographical Society would publish the few British fossil Balanidæ; the

* I feel under special obligation to Mr. Dana for several very interesting communications connected with the present subject, and for information derived from his magnificent work on the Crustacea, collected during the United States Exploring Expedition. Also to M. Bosquet, of Maestricht, for the loan and gift of several interesting fossils, described and illustrated with the utmost fidelity, in his beautiful "Monographie des Crustacés fossiles du terrain Crétacée du D. de Limbourg."

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Council has now honoured me by determining on this publication, so that these species will hereafter be more fully illustrated than they could be in the present volume. I cannot conclude this short preface, without again tendering my most grateful thanks to the Council of the Ray Society for the publication of my two volumes, and for the very kind manner in which they have acceded to all my requests.

DOWN, KENT; July, 1854.

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MONOGRAPH

ON

THE CIRRIPEDIA.

————

INTRODUCTION.

MY former volume, published by the Ray Society, treated only of the Lepadidæ, one family of the Cirripedia: I was induced to print it from having the materials ready, though this partial publication has been in some respects inconvenient. The Palæontographical Society has done me the honour to publish, with ample illustrations, the fossil species of this same family of Lepadidæ. This present volume completes my work on the sub-class Cirripedia.* I had originally intended to have published a small volume on my anatomical observations; but the full abstract given in my former volume, which will be illustrated to a certain extent in the plates appended to this volume, together with the observations here given under the Balanidæ, appear to me sufficient, and I am unwilling to spend more time on the subject. In the volume on the Lepadidæ, I gave the specific or diagnostic characters in English and Latin: I have here left out the latter, inasmuch as I have appended at the end of this volume a Latin Synopsis of all the

* The number of the British fossil species of the Balanidæ and Verrucidæ in a recognisable state is so small, that I do not know whether it will be considered worth while to publish in the Palæontographical series more detailed illustrations than are given in this volume.

1                      

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species, recent and fossil, of the whole class. To each species is added a reference to the pages and plates of my three volumes, so that the Synopsis will serve as a systematic index to the three: an alphabetical index to the present volume is also given. In the Lepadidæ, I gave an additional specific character, derived from the softer parts of the animal's body: in the Balanidæ, these parts are more alike in the different species, and I have found it impossible to give a diagnostic character thus derived. In those cases in which a Family contains but one genus, or a Genus but one species, I have assigned my reasons for the institution of such groups, but have given, as heretofore, only a single description in full: it would have been easy to have separated, by analogy, this description into one for the species, another for the genus or for the family; but as I believe such separation and subordination of the characters would have been largely conjectural, I have thought it best to act as I have done, and give, thus saving useless repetitions, only a single description, and leave it for my successors, when more genera or species are known, to separate, with such certainty as is ever possible, the generic from the specific characters.

In nomenclature, I have endeavoured rigorously to follow the rules of the British Association, and have never, at least intentionally, broken through the great law of priority. In accordance with the rules, I have rejected, that is, as compulsory, all names given before the introduction of the binomial system in 1758. I have given much fewer synonyms than is usual in conchological works; for it is impossible to recognise with any approach to certainty, several even of the common European forms, in the short descriptions given by most authors; this holds good in many cases in which figures, in appearance excellent, have been added. I assert this the more confidently, from having had the advantage of having gone over some of the Linnean synonyms with Mr. S. Hanley. I may further venture to express my conviction, that giving references to works, in which there is not any original matter, or in which the plates are not of a high order of excellence, is absolutely injurious to the progress of natural history.

Sessile Cirripedes, partly from being attached to surfaces

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NOMENCLATURE OF THE SHELL OF A SESSILE CIRRIPEDE.

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SHELL. Fig. 1.

Orifice of shell, surrounded by the sheath. Sheath formed by the alæ (a-a.) and by portions of the upper and inner surfaces of the parietes (p-p.)

N.B. In Balanus, and many other genera, the Rostrum and Rostro-lateral compartments are confluent, and hence the Rostrum has the structure of Fig. 2.

COMPARTMENTS.

Fig. 2.                                 Fig. 3.                                        Fig. 4.

Fig. 2. Compartment with two radii, serving either as a Rostrum or Rostro-lateral compartment. Fig. 3. serves as a Lateral and Carino-lateral Compartment. Fig. 4. serves as a Carina or Rostrum.

OPERCULAR VALVES.

Fig. 5. SCUTUM (internal view of).                          Fig. 6. TERGUM (external view).

Fig. 7. TERGUM (internal view).

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having very different characters, partly from undergoing a varying amount of disintegration, and partly from unknown innate causes, are extremely variable. Under the head of Variation, in the Family Balanidæ, and under the Genus Balanus, I have enlarged on this subject, and have shown that there is scarcely a single external character which is not highly variable in most of the species. As whole groups of specimens often vary in exactly the same manner, it is not easy to exaggerate the difficulty of discriminating species and varieties. It is absolutely necessary in most cases, for mere identification, that the valves of at least one specimen in a group should be disarticulated and well cleaned (for which purpose caustic potash is most useful), so that the internal characters may be examined. Whoever attempts to make out from external characters alone, without disarticulating the valves, the species, (even those inhabiting one very confined region, for instance the shores of Great Britain,) will almost certainly fall into many errors: hence it is, and can thus only be accounted for, that I have not seen one collection of British specimens with all the species, though so few in number, rightly discriminated; and in the large majority of cases, either two or three species, certainly distinct, were confounded together, or two or three varieties, as certainly not distinct, were separated from each other.

On the Names given to the different parts of Cirripedes.

In my former volume I have stated that I found it indispensable, in part owing to the extreme confusion of the nomenclature previously used, to attach new names to several of the external parts of Cirripedes. Almost all these names are applicable to the Balanidæ, or sessile Cirripedes, and to the Verrucidæ; but a few additional names are requisite, which, together with the old names, will, I hope, be rendered clear by the accompanying woodcuts. In sessile Cirripedes, the whole of that which is externally visible, may for convenience sake be divided into the

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operculum or opercular valves (valvæ operculares), and the shell (testa), though these parts homologically present no real difference. The operculum is seated generally some little way down within the orifice of the shell; but in very young specimens and in Verruca, the operculum is attached to the summit of the shell, and the shell, without the operculum be removed, can hardly be said to have any orifice; though, of course, the opercular valves themselves have an aperture for the protrusion of the cirri.

The shell consists of the basis (called the support by some authors), which is membranous or shelly, and flat or cup-formed, and of the compartments (testæ valvæ), which vary from eight to four in number, and occasionally are all calcified together.

The compartment, at that end of the shell where the cirri are exserted through the aperture or lips of the operculum, is called the carina (fig. 1); the compartment opposite to it is the rostrum,—these two lying at the ends of the longitudinal axis of the shell. Those on the sides are the lateral compartments; that nearest the carina, being the carino-lateral (testæ valva carino-lateralis), the nearest the rostrum, the rostro-lateral, and the middle one, simply the lateral compartment; but these three compartments are rarely present together. The rostro-lateral compartment, which always resembles fig. 2, and may be always known by having radii on both sides, is often absent; and not rarely the lateral and carino-lateral compartments are confounded together, or one is absent; in such cases the compartment that is left is simply called the lateral one. The compartments are separated from each other by sutures, which are often so fine and close as to be distinguished with difficulty. The edge of a compartment, which can only be seen when disarticulated from its neighbour, I have called the sutural edge (acies suturalis).

Each separate compartment consists of a wall (paries), or parietal portion (pp in woodcuts), which always grows downwards, and forms the basal margin; and is furnished on the two sides either with alæ (fig. 4), or with radii (fig. 2), or with an ala on one side and a radius (fig. 3) on the other.

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The radius* (adopting the name used by Bruguière, Lamarck, and others) differs remarkably in appearance (though not in essence) from the walls or parietal portion, owing to the direction of the lines of growth and the state of its usually depressed surface. In the upper part the radii overlie the alæ of the adjoining compartments: in outline (r, fig. 1, 2, 3), they are wedge-formed, with their points downwards; their summits (and this is often a useful specific character) are either parallel to the basis or as in fig. 1 and 2, oblique. The radii are sometimes not developed.

The alæ (so called by Dr. Gray) are overlapped by the radii and by part of the walls; they usually extend only about half way down the compartment (a fig. 3, 4, 1); their summits are either parallel to the basis or oblique. The alæ of the several compartments, together with the internal, upper, thickened surfaces of the walls, against a shoulder of which the sutural edges of the alæ abut, have been called (by Dr. Gray) the sheath (vagina). The upper and greater portion of the sheath is marked by transverse lines, caused by the exuviation of the opercular membrane, as that membrane may be called, which unites the operculum all round to the sheath, or upper internal surface of the shell.

The carina has always two alæ, as in fig. 4.

The carino-lateral and lateral compartments have always an ala on one (the rostral) side, and a radius on the other (the carinal) side, as in fig. 3.

The rostro-lateral compartment (when present) has always radii on both sides, as in fig. 2.

The rostrum has normally alæ on both sides, as in fig. 4, but very often from fusion with the rostro-lateral compartments on both sides, it has radii on both sides, as in fig. 2.

* The radii have been called by Ranzani and De Blainville, "areæ depressæ" (the parietal portions of the compartments being the "areæ prominentes"); by Poli, "areæ interjectæ;" by Gray, "sutures;" by Coldstream, "compartments of the second order," (the parietal portions being those of the first order); by some authors as "intersticia". I may here add that the scuta are the "ventral valves" of Gray, the "anterior" of Ranzani, and the "inferior opercular" of De Blainville: the terga are the "posterior valves" of Gray and Ranzani, but the "superior opercular" of De Blainville: the rostrum, on the other hand, is the "anterior valve" of Ferussac and the "ventral" of De Blainville; the carina being the "dorsal valve" of the latter author.

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The walls of the shell, the basis, and the radii, are in very many cases composed of an outer and inner lamina, united together by longitudinal septa; a set of tubes or pores being thus formed. The points of the longitudinal septa generally project beyond the laminæ, and are denticulated on both sides (see woodcut, further on;) the septa are sometimes branched, several irregular rows of pores between the two laminæ being then formed (see Pl. 7, fig. 3 b, and Pl. 10, fig. 1 g, 1 h).

Operculum, or opercular valves.—These consist of a pair of scuta and a pair of terga. They are joined to the sheath of the shell by the opercular membrane.

Scutum (woodcut 5): this valve is generally sub-triangular, and its three margins are the basal, the tergal, so called from being articulated with the tergum, and the occludent, so called from opening and shutting against the opposed valve. The angles are called from the adjoining margins, as basi-tergal, &c.; the upper angle being the apex. The scutum is ordinarily articulated to the tergum by an articular ridge (crista articularis), running up to the apex of the valve, and by an articular furrow, which latter receives the scutal margin of the tergum. The articular ridge, instead of projecting straight up from the valve, when laid flat on its external surface, often bends over to the tergal side, and is then said to be reflexed. On the internal surface of the valve, there is almost always an adductor pit or cavity (fossa adductoris), for the attachment of the adductor scutorum muscle: this pit is often bounded on its tergal and basal sides, by a ridge, called the adductor ridge (crista adductoris), which, in its upper part, is often confluent with the articular ridge. Beneath the adductor ridge, in the basi-tergal corner of the valve, there is often a lateral-depressor pit (fossa musculi lateralis depressoris), for the attachment of the so-called muscle; and this pit is sometimes furnished with crests.

Tergum, (woodcut 6 and 7):—this valve, also, has three margins, the scutal, basal, and carinal; its upper end, or apex, is sometimes beaked; on the basal margin a spur (calcar) depends; the outer surface of the valve is depressed or longitudinally furrowed (sulcus longitudinalis) in the line

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of the spur. The part called the spur is often so broad, that the name becomes not very appropriate. The angles are denominated, from the adjoining margins, as basi-carinal, or basi-scutal angle, &c. On the under side, in the upper part, there is an articular ridge, and on its scutal side, an articular furrow, receiving the articular ridge of the scutum. In the basi-carinal corner of the valve there are often crests for the attachment of the tergal depressor muscle.

Sack, Body, Cirri, Mouth.—A slit-like orifice between the opercular valves leads into the sack, in which the body is lodged. The body consists of the six (perhaps the seven) posterior thoracic segments of the archetype Crustacean; the first of these six segments (or first two, if there be seven segments) is developed on its dorsal aspect into a part, which I have called the prosoma* (see fig. 1, c, Pl. 25). There is no abdomen. The thoracic segments support six pairs of cirri. Each cirrus consists of a two-jointed pedicel, carrying two multi-articulated rami. Rarely there are articulated caudal appendages (appendices caudales) on each side of the anus. The prominent mouth consists of a labrum, palpi, mandibles, maxillæ, and outer maxillæ, the latter resembling a lower lip: these organs may be conveniently spoken of, after Milne Edwards, as gnathites. Within the sack, attached to its carino-lateral end, a folded membrane forms the branchiæ. The sheets of ova lying within the sack are called the ovigerous lamellæ.

I have often found it convenient to designate the membrane investing the body, lining the sack, &c., by its proper chemical name of chitine, instead of by horny, or other such equivalents; but when covering parts of the shell, for brevity's sake I have often spoken of it as an epidermis, but I do not believe that such is its nature. When this membrane sends into the body of the animal rigid projections or crests, for the attachment of muscles or any other purpose, I call them, after Audouin, apodemes. For the underlying true skin, I use the term corium.

Relative position of parts.—The centre of the generally flat basis, which is cemented to the supporting surface, is

* A discussion on the homologies of the different parts is given under the head of the Metamorphoses of the Balanidæ.

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properly the anterior end, and the tips of the terga, often hidden within the shell, are properly the posterior end of the external covering; but I have found it more convenient to speak of the upper and basal surfaces and aspects, which hardly admit of any mistake. A line drawn from the centre of the basis, along the middle of the rostrum to the tips of the scuta, shows the strictly medio-ventral surface of the shell; and another line drawn from the centre of the basis, along the carina, to the tips of the terga, shows the strictly medio-dorsal line; but from the crooked course of these lines, I have found it far more convenient to speak of the rostral and carinal end or aspect of the different parts of the shell; this is the more necessary with respect to the internal parts of the animal, owing to their remarkable changes of position during the metamorphosis, whence it comes that the dorsal surface of the thorax faces partly dorsally, partly anteriorly or downwards, and partly even ventrally; and the ventral surface of the whole posterior part of the thorax faces upwards or posteriorly; but when we refer these parts to the rostral, carinal, basal, and upper ends of the shell, there can be no mistake. There has moreover been great confusion in these relative terms, as applied by different authors.

When a sessile Cirripede is held in the position in which they have generally been figured, namely with the basis downwards and the scuta towards the beholder, then the right and left sides of the Cirripede correspond with those of the holder.

I have followed the example of Botanists, and added the interjection [!] to synonyms, when I have seen an authentic specimen bearing the name in question.

Every locality, under each species, is given from specimens ticketed in a manner and under circumstances appearing to me worthy of confidence,—the specific determination being in each case made by myself.

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CLASS—CRUSTACEA.

Sub-Class—CIRRIPEDIA.

Crustacea attached by the anterior end of the head, by cement proceeding from a modified portion of the ovaria; archetype composed of seventeen segments, with the three first of large size, and almost always developed into a carapace, not wholly exuviated, and capable of various movements; antennæ none; eyes rudimentary; mouth prominent, formed by the partial confluence of the labrum, palpi, mandibles, and two pairs of maxillæ; thorax attached to the internal sternal surface of the carapace, generally bearing six pairs of captorial, biramous, multi-articulated limbs; abdomen generally rudimentary; branchiæ, when present, attached to the under sides of the carapace; generally bisexual, when unisexual, males epizoic on the female; penis single, generally probosciformed, seated at the posterior end of the abdomen; oviducts none; metamorphoses complex.

Within the memory of many living naturalists, Cirripedes were universally looked on as belonging to the Molluscous kingdom; nor was this surprising, considering the fixed condition of their shells, and the degree of external resemblance between, on the one hand, Lepas and Teredo, and on the other hand, between Balanus and a Mollusc compounded of a patella and chiton. It is remarkable that this external false appearance overbore, even in the mind of Cuvier, his knowledge of their internal structure, namely, their lateral jaws, articulated appendages, and regular ganglionic nervous system, which now strike us as such conclusive evidence of their position in the great Articulate kingdom. Straus* was, I believe, the first who, in 1819, maintained that Cirripedes were most closely allied to Crustacea. But this view was disregarded, until J. Vaughan Thompson's† capital discovery, in 1830, of their metamor-

* Mémoires du Muséum d'Histoire Nat., tom. v, p. 381.

† Zoological Researches and Illustrations.

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phoses, since which time, Cirripedes have been almost universally admitted amongst the Crustaceans. It is well known, that it is hardly possible to give a definition of this great class, which shall include every member of it; nevertheless, even if the mature Cirripede alone be considered, the following characters, viz. the slight separation of the head and thorax, the latter generally bearing six pairs of appendages, and the being enclosed in a carapace—together with the periodical exuviation of the greater part of the external membranes, would, perhaps, suffice to show that it should be classed amongst Crustacea.

But it still remains undecided what rank in this class Cirripedes should hold. Before briefly discussing this point, it is indispensable to indicate their essential characters, which I will immediately attempt. For as long as it remained doubtful which was their anterior extremity, which the ventral or dorsal surface; as long as the peduncle was thought by one naturalist to be the legs, by another the abdomen, in a modified condition, it was hopeless to compare Cirripedes with ordinary Crustaceans, and assign to them their due rank.

In the larva in the first stage, an eye and two pairs of antennæ are in process of formation or are developed; here, then, according to the analogy of all Crustaceans, we have evidence of the existence of the first three cephalic segments. The mouth always consists of three pairs of gnathites, and hence again, from analogy, this part may be inferred to be formed of, and supported on, three other segments; making thus far six segments. In two Orders out of the three into which Cirripedes may be divided, namely, in the Abdominalia and Apoda, eight quite distinct segments succeed the mouth; of these the first differs slightly from the seven succeeding segments, and may, I think, be safely considered as forming the seventh (cephalic) segment. The next seven segments resemble each other in all essential respects, and are no doubt the normal, seven thoracic segments. These, in both the above orders, are succeeded by three smaller segments, which differ in structure from the thoracic segments, and must be abdominal. Hence we here have, altogether, seventeen segments. It should,

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however, be observed that in the two orders just referred to, each includes only a single species; but I know of no good reason why, on this account, their structure should be valued the less. In the third order, the Thoracica, which includes all common Cirripedes, two segments with their appendages are missing out of the eight that should succeed the mouth; from the open interval in the pupa, between the mouth and first pair of natatory legs, and from some other reasons, I believe that the two missing segments are the seventh and eighth, or last cephalic and first thoracic segments, and that they have coalesced close posteriorly to the mouth.* In the order Thoracica, the abdomen is quite rudimentary, though often still bearing caudal appendages; in the pupa, however, of this order, as in the mature animal of the two other orders, it is formed of three segments. Hence I conclude that, notwithstanding the absence of the above two segments with their appendages in the Thoracica, the archetype Cirripede may be safely said to be composed of seventeen segments.

In the classification of Crustacea, the relation and number of the segments of the different parts of the body, are viewed both by Prof. Milne Edwards† and Mr. Dana,‡ as of the highest importance. I may premise that both these authors divide the Crustacea into Podophthalmia, Edriophthalmia, and Entomostraca; Milne Edwards making a fourth legion, the Branchiopoda, and another division, including Limulus, of equal value to the above four legions altogether; whereas Dana sinks Limulus and the Branchiopoda under his Entomostraca. As far as concerns our present discussion on Cirripedes, the first three divisions, as valued by Dana, will best serve as standards of comparison; but it is not unimportant to our present purpose, as showing how difficult it is to weigh the value of the higher divisions of a Class, to observe the wide difference in opinion of two naturalists, so eminent for their knowledge of the class in question and for their high abilities.

* This question and the whole subject of the homologies of the several parts of a Cirripede, will be discussed under the head of the Metamorphoses of the Balanidæ.

† Annales des Sciences Nat., tom. xviii, p. 120, 1852.

‡ Crustacea: 'United States Exploring Expedition,' p. 1395, 1852.

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In the order Thoracica, including all common Cirripedes, the cephalic and thoracic segments are as much confounded together (but with coalescence and abortion of two middle segments) as in most Podophthalmia; but in the two other orders, the cephalic and thoracic segments are as distinct as in the Edriophthalmia. The number of the segments, however, which strictly appertain to the anterior part of the head and mouth, being only six, is an Entomostracan character; on the other hand, the first pair of cirri in the Thoracica, has some claim from their position, apparent functions, and separation from the succeeding pairs, to be said to belong to the mouth; on which view, the first nine segments would, in function, be cephalic, as in the highest Crustaceans. The fewness of the segments of the abdomen, and their not bearing in two of the orders appendages, is an Entomostracan character.

Cirripedes are permanently attached, even before their final metamorphosis, by a tissue or cement, first debouching through the second pair of antennæ, and, subsequently, in most cases, through special orifices, penetrating the anterior part of the head; this cement proceeds from glands, which certainly are modified portions of the ovarian system. This fact I consider of the highest classificatory importance, for it is absolutely the one single character common to all Cirripedes, besides such as show only that these animals belong to the articulated kingdom, and are Crustaceans. No structure of this kind has hitherto been observed in any other member of the class or kingdom. Even in the Suctorial Entomostracans, which become immoveably attached to the fish on which they prey, the males are free; and the means of attachment, as far as known, are quite different.

Both the first and second pairs of antennæ are absent in the mature animal; for the three terminal segments of the antennæ of the pupa, which may always be found cemented under the centre of the surface of attachment, are functionless, after maturity. The eyes are rudimentary, and are singular from being seated far from the anterior extremity of the head. In their rudimentary state, and in the absence of antennæ, we have characters common with certain Suctorial Entomostracans; and this similarity

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apparently arises from the fixed condition of the animals of both groups.

The carapace, which covers the dorsal surface of the larva in the first stage, in the last larval or pupal stage is developed so as to enclose, like a bivalve shell, the whole body. In the mature Cirripede, the whole external covering, whether shell and operculum, or capitulum and peduncle, can be conclusively shown to be the carapace of the pupa, modified. In thus enclosing the mouth and whole body, the modified carapace resembles that of several Entomostracans; but in being apparently formed (as I hope hereafter to show) by the development of the third segment of the head, and in consisting generally of distinct sclerodermic plates, arranged in an imbricated order, there is, I think, a closer resemblance to the same part in some of the Podophthalmia. The carapace, or portions of the carapace, being capable of other movements, besides merely opening and shutting, differs, I believe, from that of all other Crustaceans; as it likewise does* in the greater part not being periodically moulted.

Moreover, in all Cirripedes there is another striking peculiarity connected with these parts, namely, the exclusive attachment of the whole thorax or included body to the internal ventral or sternal surface of the carapace and head. In the pupa, the thorax, as in all Crustaceans, opens into, and is continuously united with, the large anterior part of the head; but from the singular fact that the thorax of the young Cirripede is developed not within the thorax, but within the head of the pupa (Pl. 30, fig. 2), with its longitudinal axis placed at right angles to that which it held in the pupal condition (the mouth and the whole exterior being developed conformably with that of the pupa), it comes to pass after the metamorphosis, that the Cirripede is, as it were, internally cut in twain (compare Pl. 25, fig. 1, and Pl. 30, figs. 2 and 3). Thus it is, as will hereafter be more fully explained, that the sack originates, and thus the body becomes attached to the internal ventral surface of the carapace and front of head.

* The carapace, however, of the Isaura, a Branchiopod, according to M. Joly ('Annales des Sc. Nat.,' 2 ser. vol. xvii, p. 293), is not moulted.

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The thorax in two of the Orders bears no appendages, but in all common Cirripedes it is furnished with six pairs of biramous, multiarticulated cirri, which have a peculiar character, different from the limbs of other Crustaceans, not being natatory, ambulatory, or branchial, but "captorial" or fitted for sweeping the water, and thus catching prey.* The cirri, at least the anterior pairs, can, besides other movements, lengthen and shorten themselves; and this Milne Edwards† states is the case with the Podophthalmia, and is considered by him as an important character. The cirri of the first pair are attached on each side close to the bases of the mandibles, and, as already remarked, have some claim to be considered as maxillipeds or mouth organs. The three or the four posterior pairs of cirri in the Balanidæ, form a series somewhat distinct from the two or three anterior pairs, thus recalling a characteristic feature in the Edriophthalmia.

The mouth is prominent, and is formed by the partial confluence of the labrum, palpi, and lower segments of the mandibles, and of two pairs of maxillæ; it is capable of movement as a whole; in this respect we are reminded of the Suctorial Entomostracans; but I believe the above type of structure of the mouth is peculiar to Cirripedes.

The alimentary canal is simple, but can be distinctly divided into—(1st) an œsophagus, singular from the bell-shaped expansion of its lower end; (2d) the stomach, which is directed forwards and then doubled back; and (3d) the rectum. There is no distinct liver. The circulation is lacunal. In one family there are well-developed branchiæ, which differ entirely in their homologies and position from these organs in all other Crustaceans. In the nervous system, the sub-œsophageal ganglions vary in concentration from that degree observed in the lower Macroura, to that in the highest Brachyoura; but the supra-œsophageal ganglions are always much less concentrated, and are even embryonic in condition; presenting a difference not observed in other Crustaceans. On the under side of the sub-œsophageal ganglion, two nerves, apparently splanch-

* M. A. Hancock, in 'Annals and Magazine of Natural History,' 2d series, 1849, p. 312, speaks of the cirri acting like a prehensile net.

† 'Annales des Sciences Nat.,' tom. xviii, p. 121, 1852.

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nic, arise, and run almost parallel and under the collar surrounding the œsophagus; they are very remarkable from their great size, and from forming a plexus together with a large branch, arising on each side from the collar close behind the supra-œsophageal ganglion,—a structure unlike anything observed in other Crustaceans. The eyes, as already remarked, are rudimentary, and singular from being imbedded at a distance from the anterior end of the animal. In the basal confluent segments of the outer maxillæ there are two orifices, leading into little sacks, which I believe are olfactory organs: again there are two other orifices on each side of the thorax, beneath the first pair of cirri, leading into sacks, with a curious elastic vesicle suspended within them; and these I can hardly doubt are acoustic organs. Of these orifices and organs, there is no trace in the same relative positions in any known Crustacean.

Cirripedes are ordinarily bisexual, in which they differ from all Crustaceans: when the sexes are separate, the males are minute, rudimentary in structure, and permanently epizoic on the females; to these latter facts we have a partial analogy in some of the Suctorial Entomostracans; but a far closer analogy in certain Rotifers, which are considered by many naturalists as Crustaceans; but to the above subject I shall almost immediately have to recur.

The male excretory organ is probosciformed and capable of the most varied movements; it is single and medial; it is seated (in the one instance in which this point can be safely judged of) at the extremity of the abdomen, and therefore near the normal position of the anus; in all these respects there is a very great difference from other Crustaceans, in which the male organs are laterally double, and are not seated at the extremity of the abdomen. In regard to the female organs, the ovarian tubes and cæca inosculate together: there are no oviducts; the ova, connected together by membrane, and so forming the "ovigerous lamellæ," become exposed by the exuviation of the lining tunic of the carapace or sack, and by the formation of a new tunic on the under side of these lamellæ; a process, I believe, unknown in other Crustaceans.

The metamorphoses are highly complex. The larva in

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its first stage bears a very close general resemblance, in having three pairs of natatory appendages, the first being uniramous and the two others biramous, and in having a single eye on its broad anterior front, to the larvæ of most Entomostracans; but I cannot avoid the belief, that this resemblance is only apparent, and not essential; and of false resemblances, how many instances occur in the animal kingdom! In the larva, when first freed from the egg, both pairs of antennæ are in process of formation within envelopes: the mouth is probosciformed and capable of movement, but is destitute of gnathites; it occupies a position between the three pairs of natatory limbs; and these limbs I must believe, for reasons hereafter to be assigned, answer (improbable as I am well aware it must at first appear) to the second, third, and fourth thoracic legs of the archetype Crustacean: the two hinder pairs of limbs apparently soon become captorial, or fitted to secure prey. Now, I cannot find in the published accounts of the larvæ of Entomostracans, any that answer to this description.

The larva in the last stage might be included in the vast class of Entomostracans: the attachment of the eyes to the singular apodemes produced inwards from the basal segment of the great prehensile antennæ, and the development of only the posterior six pairs of thoracic limbs, are its chief peculiarities: but its rudimentary mouth, owing to its transitional or pupal condition, renders the assignment of its proper rank difficult.

Having now given this short comparative sketch of the structure of a Cirripede, I may venture to express strongly my opinion, that the group is formed on a distinct type; as different from the other three or four main Crustacean groups, namely, the Podophthalmia, Edriophthalmia, Branchiopoda, and Entomostraca, as these differ from each other; the differences, moreover, being of the kind considered by the highest authorities on this subject, as the most important. It should be observed that there is no special blending at either end of the Cirripedial series, towards any one of the other main groups of Crustacea: it is hardly possible to take some one Cirripede, and say

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that it leads, more plainly than some other Cirripede, into ordinary Crustaceans. Moreover, a great range of structure, as we shall soon briefly show, is included within the group: I can adduce three or four undoubted Cirripedes, very considerably more different from each other, than any two members within the sub-class Podophthalmia, or within the Edriophthalmia, or the Branchiopoda, and quite as different as within the Entomostraca.

The opinion here expressed, that Cirripedes form a sub-class of equal value with the other main Crustacean groups, I am well pleased to find, accords with Mr. Dana's* view, who remarks that this sub-class "has so many peculiarities of structure, that it should be regarded as a distinct type, rather than a subordinate division of the third (or Entomostracan) type." M. Milne Edwards,† after dividing all Crustacea into two groups, divides one of them into four legions; and of one of these, the Entomostraca, he makes the Cirripedes a sub-group. I feel so entire a deference for any opinion on affinities or classification expressed by Milne Edwards, that I differ from him with the greatest hesitation. He does not give his reasons for assigning so subordinate a rank to Cirripedes, but I imagine it is from the nature of their metamorphoses: but if this be the case, I cannot understand why he should assign to his Branchiopods a rank equal to his Entomostracans. Moreover, I must repeat, that I do not believe that the larvæ do resemble the larvæ of Entomostracans and Branchiopods nearly so closely as at first appears to be the case. I may add, that Burmeister‡ has assigned to the Cirripedes a place amongst the Crustacea, almost equally subordinate to that given to them by Milne Edwards.

That Cirripedes have some special affinity to the Entomostraca, may be inferred from the fewness of the cephalic appendages, the biramous legs, the state of the abdomen, and the form of the carapace. Perhaps in the peculiar state of confluence of the lower segments of the gnathites,

* 'Crustacea: United States Exploring Expedition,' p. 1407, 1852.

† 'Annales des Sciences Nat.,' tom. xviii, p. 120, 1852.

‡ 'Beiträge zur Naturgeschichte der Rankenfüsser,' 1834.

2                        

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in the aborted antennæ, the rudimentary eyes, and in the minute parasitic males (when such exist), there is a more direct relation to the Suctorial division of the Entomostraca; but some of these resemblances are probably only analogical, resulting from the fixed condition of both groups. It should not be overlooked, that out of the three orders into which Cirripedes may be divided, in the two latter, the mature animal presents hardly any resemblance to an Entomostracan. From the distinct presence in either pupa or mature animal of the fourteen segments of the cephalo-thorax; from the apparent composition of the carapace, as will be subsequently explained; and from the concentrated condition of the nervous system, one is led to glance at the higher Crustacea; and here we shall find amongst the Podophthalmia, one aberrant group of low organisation, namely, that including Phyllosoma, Amphion, &c., in which more points of resemblance to Cirripedes may be detected, than, as I believe, in any other group whatever; for we here see that remarkable elongation of the head in front of the mouth, so eminently characteristic of Cirripedes; we have a carapace overlapping the thorax, which is sometimes free beneath; we have the abdomen sometimes almost obsolete; we have biramous legs; and especially we have the posterior cephalic and the first thoracic appendages more or less rudimentary and obsolete; and this, I infer from Mr. Dana, is a very rare phenomenon, though characteristic of all ordinary Cirripedes, in which the seventh and eighth segments with their appendages have disappeared. In the order including Phyllosoma, &c., namely, in the Macroura, the ganglions which give nerves to the five posterior thoracic limbs, are distinct from the great sub-œsophageal ganglion which supplies the several anterior appendages; this is the case with those Cirripedes in which all the infra-œsophageal ganglions are not concentrated into one. In the Macroura and Brachyoura, the first pair of legs almost always differs in structure from the others, so does the homologous or second cirrus in Cirripedes differ from the four succeeding pairs; in some few Macroura, the second leg is antenni-formed, so in some few cases is the homologous (or third) cirrus; J. Vaughan Thompson was even struck by the

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resemblance in the curious, doubly pectinated spines on the anterior limbs of Mysis (allied to Phyllosoma*), and on those of many Cirripedes: these several latter resemblances may be small, but certainly I do not believe that they are accidental. Now the little group of Crustaceans, which includes Phyllosoma, &c., has lately been placed, by Milne Edwards, as a satellite amongst the Macrourous Podophthalmia; it leads into the Stomopoda, and likewise, as has been noticed by many authors, into the sub-class Branchiopoda, which latter sub-class is considered by Mr. Dana as only a part of the Entomostraca; this group, therefore, exhibits affinities radiating in several directions, and amongst these lines of relationship, one more must, I believe, be added, plainly directed towards the Cirripedia.

One naturally wishes to ascertain how far Cirripedia are highly or lowly organised and developed; but in all cases this, as it seems to me, is a very obscure enquiry. Mr. Dana considers that, in Crustacea, the greater or less centralisation of all the appendages round the mouth is the main sign of high development; on this view, the anterior part of a Cirripede, from being so much elongated, must be considered as very low in the scale; the whole posterior part of the body, on the other hand, is, in ordinary Cirripedes, brought close to the mouth; but this is effected by the abortion of the seventh and eighth segments of the cephalo-thorax and of the whole abdomen, and so, I presume, would not, in Mr. Dana's estimation, raise the class much in the scale. Von Baer† considers that the perfection of the type of any animal is in relation to the amount of "morphological differentiation" which it has undergone; on this view, Cirripedes ought to stand high in the scale, for they differ much morphologically from the type of the class to which they belong; as indeed is shown by the long time that elapsed before their true position, namely amongst the Crustacea, was even suspected; but something more must, I think, be added

* M. Martin St. Ange ('Mémoire sur l'Organ. des Cirripèdes,' 1835, extrait des 'Savans Etrangers,' tom. vi) has compared the mouth of Lepas with that of Phyllosoma, and has given comparative figures; but the resemblance is founded, I believe, on quite false homologies.

† English Translation, in 'Scientific Memoirs,' 1853, vol. i, p. 228.

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to Von Baer's definition; for, to take as an example the eyes of a Cirripede,—as seen in the first larval stage, there is only one eye, and that most simple; in the pupa there are two, both compound, and furnished with complicated muscles; lastly, in the mature animal there are still two, but of very minute size, often almost confluent, and of the simplest structure; hence, then, there has been much morphological differentiation, but it is almost a contradiction in terms to speak, in relation to such a case, of perfection of type; and what has happened to one organ, might happen to other organs, and so to the whole animal. Lastly, under a physiological point of view, and taking the Balanidæ as the most perfect type of the class, the sub-œsophageal portion of the nervous system is highly concentrated; the organs of sense, excepting the eyes, seem more largely developed than in ordinary Crustaceans; the circulating system is of the simplest kind, being only lacunal; special Branchiæ, however, are developed by the metamorphosis of, as I believe, a special organ, occurring only in the Lepadidæ; the digestive organs are very simple, from not having any distinct liver; the generative system is very low, for both sexes are generally united in the same individual; and the testes and ovaria closely resemble each other. On the other hand, the thoracic limbs are, to a considerable extent, specialised in their structure and functions; only the three posterior pairs strictly resembling each other. Lastly, the dermal and muscular systems are complicated, and not, to use Professor Owen's term, by mere vegetative repetition, as will be obvious to any one who will study the beautifully constructed and modified carapace—that is the operculum, shell and basis—of a Balanus. On the whole, I look at a Cirripede as a being of a low type, which has undergone much morphological differentiation, and which has, in some few lines of structure, arrived at considerable perfection,—meaning, by the terms perfection and lowness, some vague resemblance to animals universally considered of a higher rank.

It has been seen that I divide the Cirripedia into three orders,—the Thoracica, Abdominalia, and Apoda; between

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which the fundamental difference consists in the limbs or cirri being thoracic in the first; abdominal in the second; and entirely absent in the third. For the sake of showing the range of character in Cirripedes, to which allusion has been made, I will briefly indicate the leading differences in each order. In the Thoracica, three families are included,—the Balanidæ, or sessile Cirripedes, the Verrucidæ, remarkable from their quite asymmetrical shell, and the Lepadidæ, or pedunculated Cirripedes. The great difference in external appearance between these three families is known to all naturalists. Even within the one family of Lepadidæ there are great differences in external appearance, as will be admitted on comparison of Lepas, Pollicipes, Conchoderma, &c.; but we have also important internal differences, as in the case of Anelasma, in which the cirri are barely articulated, and are not capable of seizing prey, whilst the mouth is almost probosciformed, with the outer maxillæ and palpi rudimentary: still more important are the differences in Alcippe, in which the cirri of the first pair act as brushes; the second, third, and fourth pairs being quite aborted; and the fifth and sixth pairs consist only of four segments, with one of the two normal rami converted into a crenated, button-like projection, for the sake apparently of triturating food; Alcippe, also, is very remarkable in being destitute of a rectum and anus. In this same genus Alcippe, in Ibla and Scalpellum, there are either separate males or Complemental males, some of which are so utterly abnormal in their characters, that by no definition which I could frame, could they be included even in their proper Order, much less in their proper Family.

In the second order of Abdominalia (Pl. 23 and 24) the seventh or last cephalic segment is quite distinct, and bears rudimentary organs, answering to the first pair of maxillipeds of ordinary Crustaceans, of which organs, and of the segment supporting them, there is no trace in the Thoracica: the seven succeeding thoracic segments are destitute of any appendages; but the three segments of the abdomen bear three pairs of cirri. The mouth is peculiar in the labrum being developed into very large, moveable, lancet-formed organ; and the lower end of the œsophagus is armed with

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beautiful discs of teeth, and brushes of hairs,—a structure confined to this order. The male resembles the male of Alcippe; and the latter genus seems to be the connecting link between the Thoracica and Abdominalia. But the most important character of this latter order, in which it differs from Alcippe, and all other known Cirripedes, is in its metamorphoses; all the first changes are merely indicated by changes in form in an egg-like larva, without the development of distinct organs; and the last, or pupal condition, which is attained within the sack of the parent, is very peculiar, by the entire absence of natatory limbs.

The third order of Apoda is the most peculiar of all; it contains, like the last, only one known species: the most acute naturalist, I am convinced, if he had not made the class his special study, would never even have suspected that this animal was a Cirripede. We see much magnified in Pl. 25, fig. 7 a naked, plainly-articulated animal, resembling the larva or maggot of a fly, attached by two threads; and these threads, on analysis, can be clearly shown to be the last rudiment of the carapace, specially modified. The last cephalic, the seven thoracic, and the three abdominal segments, are all equally destitute of appendages. The mouth is suctorial, and constructed on a plan unlike, I believe, anything known in the articulate kingdom; for the mandibles and maxillæ have rotated on their axes, and stand back to back; they can act only by tearing open a slit, and this action is performed in a hood, formed by the confluence of the broad palpi and labrum. Although the œsophagus is distinct, there is no stomach or anus. Lastly, owing to there being no carapace, the ova are developed, differently from in all other Cirripedes, within the thorax.

I will close this preliminary discussion on the confines and type of the sub-class, by recalling attention, now that a sketch has been given of the three Orders, to the remark before made, that a wide range of structure is included within it, and by reurging that the Cirripedia should be ranked, not as one of the subordinate groups, but as one of the main divisions of the Crustacea.

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On the Sexual Relation of Cirripedes.

Cirripedes are commonly bisexual or hermaphrodite, but in Ibla, Scalpellum, and Alcippe, members of the Lepadidæ in the order Thoracica, and in Cryptophialus in the order Abdominalia, the sexes are separate. As two of these genera were described in my former volume, and two others (Alcippe and Cryptophialus) are described in this volume, I may as well here give a brief summary of the facts as yet known on this very curious subject. The Males, in the above four genera, present a wonderful range of structure; they are attached in the usual way by cement proceeding from the not-moulted antennæ of the pupa, to different parts, in the different species, of the female. These males are minute, often exceedingly minute, and consequently generally more than one is attached to a single female; and I have seen as many as fourteen adhering on one female! In several species the males are short-lived, for they cannot feed, being destitute of a mouth and stomach. As the females are longer lived, successive crops of males, at each period of propagation, become attached to her. It is the females in the above genera which retain the characters of the genus, family, and order to which they belong; the males often departing widely from the normal type. Some of the males are rudimentary to a degree, which I believe can hardly be equalled in the whole animal kingdom; they may, in fact, be said to exist as mere bags of spermatozoa. So widely do some of them depart in every character from their class, that twice it has happened to me to examine specimens with a little care, and not even to suspect, until a long period afterwards, that these males were Cirripedes.*

* In my volume on the Lepadidæ (p. 200) in searching for analogies for the permanently epizoic and rudimentary condition of the male Cirripedes, I quoted two cases, which I believe are now known not to be analogous; namely, the Syngamus trachealis of Von Siebold, and the worm-like Hectocotyle, which latter was quite lately supposed to be a male Cephalopod, but has now been ascertained to be only one of the arms of the male wonderfully adapted and organised as a sperm-receptacle. The Asplanchna, the mouthless male of a Rotifer, (p. 292) alone remains for me.

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In Scalpellum Peronii, and villosum, the males are but little abnormal, for if classified independently of their sexual relations, they would be considered as immature specimens of a new genus, standing next to Scalpellum; in Scalpellum rostratum, the male would form another and rather more distinct genus. The males, in the latter, are attached to the other sex, between the basal edge of the labrum and the adductor scutorum muscle; but in S. Peronii and villosum they are attached lower down, in the furrow between the two scuta, and are thus protected: in these three species, the internal parts of the male present nothing particular. In Ibla, the males are attached low down within the sack of the female; they may be said to consist of a mouth surmounted on a long peduncle, for there is no capitulum or general covering, and the whole thorax is in a rudimentary condition, the cirri being reduced to two distorted pairs. As these males certainly moult several times and grow a little, they must feed; and as they have no cirri fit for action, they must seize their food by the contortions of their peduncle, which we know homologically consists of the three first segments of the head. The movements of the peduncle must, also, supply those of the probosciformed penis, almost invariably present with other Cirripedes, but here absent. If compelled to class these males without regard to the female, great difficulty would be experienced; we could hardly place in the family of the Lepadidæ, a Cirripede without a capitulum, and without cirri, those very organs which give their name to the class, and with a thorax reduced to the dimensions of a lower lip; yet, if the presence of a peduncle did determine the classifier to place these males amongst the Lepadidæ, then undoubtedly the character of the mouth, &c. would fix their position next to Ibla.

The males of Scalpellum vulgare, ornatum, and rutilum, resemble each other in all essential points, and differ wonderfully in appearance and structure from all ordinary Cirripedes. They consist of a minute flattened bag with a small orifice at the summit, and at the lower end attached by the cemented pupal antennæ. On each side of the orifice, there is a pair of calcareous beads, representing the two

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scuta and two terga of ordinary Cirripedes; and between the scuta a minute black eye is generally conspicuous. In S. ornatum the beads, I may remark, on the two sides are not equal; those either on the right or on the left side, being larger than those on the opposite side, so that the animal externally is asymmetrical. Inside, within a tubular sack, the thorax is lodged, supporting four (instead of six) pairs of limbs; and these, instead of forming biramous, multiarticulated, captorial cirri, are reduced to almost a rudiment, supporting a few long sharp spines, which apparently act only as defensive organs. At the end of the thorax there is seated a large abdominal lobe, which does not occur in the other sex. Hence the thorax, though rudimental, has been specially modified. Of the mouth and stomach there is not a vestige. Constructed as these males are, assuredly they have no claim to be ranked amongst the Lepadidæ or pedunculated Cirripedes; nor is it possible to class them in any group whatever of ordinary Cirripedes. In S. vulgare the males are attached, often several together, to the extreme edges of the two scuta, and therefore immediately over the orifice leading into the sack; in S. rutilum and ornatum, they are attached in concavities on the under side of both scuta, just above the depression for the adductor scutorum muscle. In the former of these species, the pit for the reception of the male is formed by shelly matter not having been deposited over a certain space on the under side of the valve; and the pit is converted by a covering of membrane into a pouch. As there are two scuta so there are two pouches, in each of which a male is lodged; hence, according to the Linnean nomenclature, Scalpellum ornatum may be said to belong to Diandria monogynia. As these males, from being mouthless, soon die, they are succeeded by successive pairs; the pupa being led by a wonderful instinct to crawl into the pouch, and there undergo its metamorphosis.

Lastly, the males of Alcippe and Cryptophialus (Pl. 23, fig. 19, and Pl. 24, fig. 19) are remarkable for their similarity to each other, considering the essential dissimilarity of the two females. The females live in cavities which they excavate in the shells of Molluscs, and within which they are attached by a horny disc; this disc is the only part

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of the outer integument which is not frequently moulted, and, apparently in consequence, the males are attached to its edges. It results from this position, that the males are protected by being enclosed within the cavity excavated by the female; and it further results, that the males are attached at a considerable distance from the orifice of the sack of the female, into which the spermatozoa have to be conveyed; and to effect this, the probosciformed penis is wonderfully developed, so that in Cryptophialus, when fully extended, it must equal between eight and nine times the entire length of the animal! These males, like those last mentioned of Scalpellum, consist of a mere bag, lined by a few muscles, enclosing an eye, and attached at the lower end by the pupal antennæ; it has an orifice at its upper end, and within it there lies coiled up, like a great worm, the probosciformed penis, and beneath it a single testis, with a single vesicula seminalis. These organs complete the whole organisation of the male; for there is no mouth, no stomach, no thorax, no abdomen, and no appendages or limbs of any kind. Yet all these parts are present in the female. I know of no other instance in the animal kingdom of such an amount of abortion. The whole exterior of these males evidently is composed, as in all ordinary Cirripedes, of the three first cephalic segments; of the fourteen succeeding segments of the archetype Cirripede we have not a vestige, excepting the probosciformed penis, which, from analogy, should arise from the ventral apex of the seventeenth segment, the first three segments of the head being counted in the seventeen. Here, then, fourteen out of seventeen segments have aborted, the tip of the seventeenth having coalesced with the third cephalic segment! I am tempted just to notice the case of Proteolepas, in the order Apoda, as showing, within the limits of the same sub-class, a wonderful amount and diversity in abortion; for in Proteolepas, the three anterior cephalic segments are reduced to the merest rudiment, encasing the cement-ducts, the fourteen succeeding segments being unusually well developed; whereas in the above described males, we have just seen the three anterior segments fully developed, whilst the fourteen succeeding segments

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are lost or have coalesced with the others; so that within the same sub-class all seventeen segments of the archetype have almost disappeared.

It may be asked how I know that the several above described rudimentary epizoons are really the males of the Cirripedes to which they are attached. Even if the whole course of the metamorphoses had not been known in three of the cases, the mere fact of these epizoons being cemented by the three terminal segments of their peculiar, pupal antennæ, would have been sufficient to have shown that they belonged to the class of Cirripedes. In nearly every case, I was able to demonstrate, and not in one or two but in many specimens, that these epizoons were males; and as in several instances the spermatozoa were developed, and as, notwithstanding, in no instance was there a vestige of ova or ovaria, it may safely be concluded that they were not hermaphrodites, and therefore required females of some kind. If these epizoic Cirripedes had been independent animals, as they all belong to the same sub-class, and all have such peculiar habits, it might have been expected that they would have shown some special affinity towards each other; but this is not the case; the epizoon of Ibla is more nearly related to Ibla, and the epizoon of Scalpellum more nearly related to Scalpellum, than are these epizoons to each other. If the several epizoons were classed by themselves, they would be grouped in divisions, corresponding with those of the Cirripedes on which they are attached, which is just what might have been expected if these latter were their females. There are, also, many special relations between the male epizoons and the Cirripedes to which they are attached; thus, the mouth of the epizoon of Ibla, is so like the mouth of Ibla, which is peculiar in several respects, that I should easily have recognised it as belonging to a member of that genus. Scalpellum villosum is remarkable as one out of only two or three members of the whole Family, which is destitute of caudal appendages, so is its male epizoon; again, S. villosum is unusually spinose, so is its male epizoon; on the other hand, Scalpellum ornatum is remarkably smooth, so is its male epizoon; and I could give other similar instances. Will it be believed that these

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coincidences are accidental, and that the epizoons have no special or sexual relation to the Cirripedes to which they are attached?

One other instance of coincident structure is so important, that it must, even in this sketch, be noticed; the prehensile antennæ of the pupa are most important and complicated organs, and differ in the different genera of the same family; they are preserved in a functionless condition throughout life, and in two instances I was able accurately to compare these organs in the epizoon and in the Cirripede to which it was attached, and they were identical in every particular. The full force of the excessive improbability of this resemblance, and of the above coincidences in structure, on the supposition of the epizoon and its support not being sexually related, will hardly be perceived without referring to the facts given in detail in my former volume.

Lastly, in the case of Cryptophialus (and indirectly in that of Alcippe) the nature of the male epizoon is, I think, actually demonstrated; for I traced both it and the female or ordinary form of Cryptophialus, through the same several larval stages, from the egg, enclosed within the sack of the female, to the pupa and mature animal. Moreover, if the male nature and sexual relation to the supporting Cirripede, be admitted in any one of these epizoons, then so close is the agreement in habits, and to a certain extent in structure, in all the foregoing epizoons, that probably no one admitting one instance would dispute the others, and further evidence would even be superfluous. Indeed, had it not been for the following facts, I should not have brought forward, either here in abstract, or in other places in detail, so many arguments and so much evidence.

I have as yet not entered in detail on the sex of the supporting Cirripede: in Cryptophialus, Alcippe, and in one species of Ibla, I was able to demonstrate in many specimens, that all the male organs, internal and external, were entirely absent; and consequently that these Cirripedes were exclusively female. In Scalpellum ornatum, also, there is no trace of external male organs (the state of the four dried spe-

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cimens not allowing the internal organs to be examined), and there cannot be any reasonable doubt that this species likewise is exclusively female. It should be borne in mind that the male organs, external and internal, are most easily discovered, and that in the above cases I had an abundant supply of excellent specimens. On the other hand, in Ibla Cumingii, and in four species of Scalpellum, I was able to demonstrate in the supporting Cirripede the presence of all the male organs, as well as of the female; and in the vesiculæ seminales of several specimens, both in the Ibla and in Scalpellum vulgare, spermatozoa were contained; the male organs, however, not being very amply developed. These species, consequently, are not exclusively female, but are hermaphrodite, though having male epizoons attached to them. This statement, I am well aware, is enough, at first, to cast a doubt on all that I have said; but let any one reflect on the evidence, of which I have here given a summary, and which has been elsewhere given in full, and I think he must admit that at least those epizoons which are exclusively male, and which are attached to Cirripedes exclusively female, are sexually related and form one species; but if he admit this, he cannot possibly escape from the conclusion that some of the other epizoons, for instance that of Ibla quadrivalvis; are the males of the hermaphrodites to which they are attached,—these epizoons not exclusively impregnating the ova of a female, but aiding the self-impregnation of an hermaphrodite. Hence I have called these males Complemental Males, to show that they do not pair with a female, but with a bisexual individual. Nothing strictly analogous is known in the animal kingdom, but amongst plants, in the Linnean class, Polygamia, closely similar instances abound.

In the series of facts now given, we have one curious illustration more to the many already known, how gradually nature changes from one condition to the other,—in this case from bisexuality to unisexuality. Finally, in the four genera so often named, we meet the following several cases, some of them even the most diverse, occurring in closely allied species. (1st,) a female, with a single male (rarely with two) permanently attached to her, protected

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by her, and capable of seizing, by the movements of its pedunculated body, any minute animals or substances found within her sack; (2d), a female with successive pairs of short-lived, mouthless males, inhabiting pouches on each side under her scutal valves; (3d), a female with many, in one instance fourteen, short-lived males, destitute of mouth, thorax, and appendages, but furnished with a stupendously long male organ, attached to a thickened portion of her outer integuments, but lying within the cavity which she has excavated; (4th), an hermaphrodite with a male attached within the sack, capable of feeding itself, as in the first case; (5th), an hermaphrodite with from one to three males, organised like ordinary Cirripedes, and apparently capable of seizing prey in the common way; and attached between the scuta, and thus protected; (6th and lastly), an hermaphrodite with from one or two up to five or six, short-lived, mouthless males, like those in the second case, attached in one particular spot, on each side of the orifice leading into the sack.

I.—ORDER THORACICA.

Cirripedia having a carapace, consisting either of a capitulum on a peduncle, or of an operculated shell with a basis. Body formed of six thoracic segments, generally furnished with six pairs of cirri; abdomen rudimentary, but often bearing caudal appendages; mouth with the labrum not capable of independent movements; larva firstly uniocular, with three pairs of legs, lastly, binocular, with six pairs of thoracic legs.

In the sketch of the three Orders given in the Introduction, it will have been seen that the differences in their structure are so great, that it would have been hardly possible to have given a single blended account of the whole Class. But as all common Cirripedes are included in the present Order, here would have been the natural place for a full description of their external and internal structure. Having, however, been necessarily, yet perhaps unfor-

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tunately, led to give, in my former volume, a description of this kind of the Lepadidæ; and as it is necessary to give a similar account of the other great family of the Order, namely, the Balanidæ, I have found it more convenient to make this latter account comparative and supplemental to the former one on the Lepadidæ, and so serve for the Order, rather than attempt to give a separate description in full of it. For this latter plan would have involved much useless repetition, as, on account of the many exceptions and limitations necessary to almost every statement, there is little choice between a description of great length and a mere diagnostic character of the Order, such as I have given above.

The Thoracica may be divided into three very natural Families, of nearly equal value; firstly, the Balanidæ, or sessile Cirripedes, which may be subdivided into two sub-families, also very natural, the Balaninæ and Chthamalinæ; secondly, the Verrucidæ, containing only one genus; and thirdly, the Lepadidæ, or pedunculated Cirripedes. These three families differ from each other, besides in mere external appearance, almost exclusively in the relation of the different portions of their external covering or carapace, and of the muscles moving such portions. In the Balanidæ, the four opercular valves surrounding the orifice leading into the sack, are capable of other movements, besides being opened and shut; whereas all the other valves are immoveably united together. In the Lepadidæ, the valves answering to the opercular valves, are furnished with a muscle only for shutting them; whereas the peduncle answering to the basis in the Balanidæ is capable of various movements. In the Verrucidæ the shell is singularly asymmetrical; only half of the operculum (either the right or the left side, this varying even in the same species) being moveable; the other half being immoveably united to the remaining valves; and the whole shell has only one muscle serving to shut the moveable half of the operculum. All the internal parts and organs are very similar in the above three Families. If, however, the internal structure of one of the two sub-families, into which the Balanidæ may be divided, namely, of the Balaninæ, be compared with that of the Lepadidæ,

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several important differences may be detected;—on the one hand, in the Balaninæ, the presence of branchiæ, the extremely complicated cementing apparatus, the difference in structure between the third and succeeding pairs of cirri, the large palpi, the notched labrum, and the laterally double teeth of the mandibles;—and on the other hand, in the Lepadidæ, the presence of ovigerous fræna, caudal appendages, bullate labrum, and often prominent olfactory orifices. But if the Lepadidæ be compared in these several respects with the other sub-family, or Chthamalinæ, which cannot possibly be removed out of the family of Balanidæ, many of these differences break down and disappear, in some or all of the species.

The Lepadidæ include, as has previously been noticed, a much greater range of difference than the Balanidæ; and this is what might have been expected, for it is the most ancient family, and extinction has done its work, separating genera, which, in accordance to analogy, we may suppose were once more nearly connected by intermediate forms. The Lepadidæ, in one sense, may be taken as the type of their order; for they have undergone less "morphological differentiation;" that is, they differ the least from the last larval stage, and seem to give the most general idea of a Thoracic Cirripede. On the other hand, if we mean, as some authors do, by the word type, that form which, in the group in question, has been most modified, and illustrates every peculiarity of its class in the strongest manner, then we must look to the Balaninæ, and to its typical genus, Balanus, for the most Cirripedial form. In this genus the different portions of the carapace differ most, and subserve to a certain extent different ends, and in minute structure are most complicated; here the cementing apparatus, which offers the main characteristic of the whole sub-class, is most complex; here the several pairs of cirri differ most from each other in structure and action; here the peculiar branchiæ (organs apparently derived from the modification of another organ, itself confined to Cirripedes, viz., the ovigerous fræna) are best developed; here the nervous system is most highly concentrated; and, lastly, here we meet with the largest and most massive species of the whole group.

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1. Family BALANIDÆ, (or Sessile Cirripedes.)

Cirripedia without a peduncle; scuta and terga furnished with depressor muscles; other valves united immoveably together.

TABLE OF CONTENTS.


Page
Structure of shell . . . . . . 34
       ,,      of the compartments . . . . . . 43
       ,,      of the radii . . . . . . 45
       ,,      of the alæ and sheath . . . . . . 47
       ,,      of the basis . . . . . . 49
       ,,      of the scuta and terga . . . . . . 51
Growth of whole shell and minute structure of valves . .
54
Sack, muscles of . . . . . . 61
Branchiæ . . . . . . 63
Thorax and body . . . . . . 65
Muscular system . . . . . . 68
Cirri, muscles of . . . . . . 71
Mouth . . . . . . 74
Cirri . . . . . .
81
Caudal appendages . . . . . . 85
Alimentary canal . . . . . . 85

Page
Circulatory system . . . . . . 87
Nervous system . . . . . . 88
Eyes and vision . . . . . . 93
Acoustic organs . . . . . . 95
Olfactory organs . . . . . . 97
Male organs of generation . . . . . . 97
Female organs of generation . . . . . . 100
Metamorphoses and homologies . . . . . . 102
Larva, first stages . . . . . . 103
Larva, last or pupal stage . . . . . . 110
Act of metamorphosis . . . . . . 126
On the homologies of the carapace . . . . . . 131
Cementing apparatus . . . . . . 133
Classification and variation . . . . . . 152
Rate of growth, exuviation, &c. . . . . . . 156
Geographical range and habitats . . . . . . 159
Geological history . . . . . . 172

Almost every one who has walked over a rocky shore knows that a barnacle or acorn-shell is an irregular cone, formed generally of six compartments, with an orifice at the top, closed by a neatly-fitted, moveable lid, or operculum.* Within this shell the animal's body is lodged; and through a slit in the lid, it has the power of protruding six pairs of articulated cirri or legs, and of securing by their means any prey brought by the waters within their reach. The basis is firmly cemented to the surface of attachment. The whole shell, basis, and operculum consists, as we have already seen, of the first three segments of the head, modified into a singularly constructed carapace, which encloses

* The best published description of the structure of the shell of a sessile Cirripede, is given by Dr. Coldstream, in the 'Encyclopædia of Anatomy and Physiology,' article 'Cirrhopoda.'

3                    

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the mouth and rest of the body. The anterior extremity of the shell is situated in the centre of the basis, where indeed, by due care, the antennæ of the pupa may be always detected; and the posterior extremity is directed vertically upwards.

When the shell of a sessile Cirripede or barnacle, for instance, of a Balanus, is first examined, the structure appears extremely complicated; but this can hardly be considered as really the case. The structure will, I think, be best understood by recalling to mind that of Pollicipes,—the oldest known genus, from which, in one sense, all ordinary Cirripedes, both sessile and pedunculated, seem to radiate. I must premise, and the fact in itself deserves early notice, that the homologies of the several parts in the pedunculated and sessile Cirripedes admits of no doubt,—that is, if amongst the pedunculated, the genus Pollicipes, or certain species of Scalpellum, be taken as a standard of comparison.* The peduncle corresponds with the basis, as may be clearly seen, if a Pollicipes with a short peduncle, and a Balanus, with a deep cup-formed or cylindrical basis be compared, for the contained parts are similar, and both grow at their upper edges upwards and outwards. Secondly, the valves round the lower part of the capitulum of a Pollicipes, though generally much more numerous, and forming more than one whorl or circle, and not so closely packed together, answer to the compartments forming the shell of a sessile Cirripede; this is shown by their lateral and downward growth, by their upper ends generally projecting freely above the cavity in which the animal's body is lodged; and in the case Pollicipes mitella, by an actual resemblance in outline, some being triangular, some broad at the upper end, and some sub-rhomboidal, and, lastly, in the manner in which they slightly overlap and indent each other: moreover further resemblances in the relative position and even in the size of the several valves, will hereafter be pointed out between certain sessile genera amongst the Chthamalinæ

* Dr. J. E. Gray long ago observed these homologies. If Lepas be taken, the comparison is not quite so simple, owing to the growth of all the valves in that genus being upwards; but in several species of Scalpellum we may see the intermediate steps between the normal downward growth of the valves in Pollicipes, and the abnormal upward growth in Lepas.

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and certain genera of the Lepadidæ. Thirdly, the scuta and terga in Pollicipes, so strikingly resemble in manner of growth—in position relatively to the animal's body—in shape—and even in being articulated together, the valves which form the operculum or lid of sessile Cirripedes, that their identity is at once obvious.

It may be well here further to premise, that apparently none of the sutures in the shells of Cirripedes correspond with the articulations between the three archetype cephalic segments, of which the whole shell is formed; or with the eight elemental pieces, of which each separate segment in the archetype crustacean is known to consist. But, as I believe, the several valves in the shell of a Cirripede are homologous, or at least analogous, with the sclerodermic plates,* of which the carapace of the Podophthalmia is formed; with this difference, that in the latter they become, after their first formation, united together into a single piece, and are thus moulted as a whole; whereas in Cirripedes, the valves or sclerodermic plates are not moulted, but continue to be added to throughout life.

In Pollicipes, there is no difficulty in understanding the growth of the lower valves of the capitulum, especially if a species be taken in which these valves stand a little way apart: at each period of growth, they are added to at their basal edges and a little way up both sides; at the same time, a new membrane connecting them together is formed, the old membrane disintegrating, or being left hanging in tatters to the last zone of growth. Now if we look at the shell of a sessile Cirripede, there is no essential difference in the growth of the compartments or valves; all grow downwards and laterally; but they overlap each other much more laterally than in Pollicipes, and the connecting membrane is in most parts reduced to a mere film jammed in between the valves; but, in the case of the opercular membrane, it still remains wide, and is periodically moulted.

In the annexed woodcut (fig. 1), of the rostrum of Balanus Hameri, the downward growth and the lateral

* Milne Edwards, 'Annales des Sciences Naturelles,' tom. xviii, (1852), p. 236.

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growth on both sides is plain. The modified sides (rr) for convenience sake, have been called the radii; they invariably overlap the adjoining compartments. The middle part

Fig. 1                                       Fig. 2                                     Fig. 3

p, p, Parietes; r, r, Radii; a, a, Alæ.

Fig. 1, Rostrum with two radii, serving in the Chthamalinæ for rostro-lateral compartments.

Fig. 2, always serving for lateral and carino-lateral compartments.

Fig. 3, Carina, serving in the Chthamalinæ, also, as a rostrum.     

(p), has been called the wall, or parietal portion: in the specimen figured, the walls and radii are distinctly separated, but in some cases, especially amongst the Chthamalinæ, the lines of growth are absolutely continuous from one to the other. In fig. 2 of a Lateral compartment of the same Balanus, we have the same essential structure; but the left side (a) is more protuberant, and is hollowed out in its lower half; it is, also, more distinctly separated from the parietal portion: this side has for convenience been called the ala; it is invariably overlapped by the adjoining compartment: in some few cases, as in Pachylasma, the ala is not hollowed out in its lower part, and from being added to in a straight line along its whole edge, with the lines of growth continuous with those on the wall, it differs hardly at all in appearance from a radius. Lastly, in fig. 3 of the carina, or compartment facing the rostrum, we have alæ (aa) on both sides; these being, as in all cases, overlapped by the adjoining compartments.

Now, the compartments in the shell of every sessile Cirripede, are without exception constructed on the above three simple patterns. In number, they are 8, 6 or 4, or all confluent together.

Considering this simplicity in growth and form of the separated compartments, it seems at first surprising that

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the construction and enlargement of the whole shell in Balanus, should long have been viewed as a difficulty. But the radii, from growing against rectangular indentations, or rather furrows, in the opposed compartments, come to be set a little inwards; and their external surfaces assume a very different appearance from the wall-portions of the compartments, which grow against the surface of attachment. In different species, the summits of the radii (and of the alæ) grow either very much more obliquely than in the species figured, or more squarely—that is, they extend from tip to tip of the adjoining compartments, parallel to the basis. In this latter case, and when the surfaces of the radii differ considerably in appearance from the walls, as in Balanus tintinnabulum (Plate 1), I am not at all surprised that the radii should have been described as separate elements, and called "areæ interjectæ," or "compartments of the second order:" for the shell of this Balanus seems to be composed of six wedges with their points upwards, namely, the parietal portions of the compartments, and of six other narrower wedges, the radii, with their points downwards; and the fact that these latter wedges consist simply of the sides of the parietal portions, modified by growing against the adjoining compartments, is completely masked. I should add, that sometimes the radii are not developed, which simply means that the overlapping lateral edges of the compartments have not been added to during growth.

The alæ are originally developed at the period of the metamorphosis, as slight lateral protuberances in the upper part of the compartments; from being overlapped, and therefore not exposed to external influences, and from growing (as in the case of the radii) against rectangular indentations or furrows in the adjoining compartments, they generally assume an extremely different appearance from the parietes, and might naturally be thought to have a very different nature. But the alæ in all cases (as is obvious in Pachylasma) are nothing but the protuberant lateral edges of the compartments, rendered thin and modified during growth. In order that the margins of the alæ should be received in an indentation, the upper internal surfaces of the walls of the

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recipient compartments are thickened all round, excepting where they receive the alæ. This thickened, upper, internal portion of the walls or shell, together with the alæ themselves, form the part called the sheath. The sheath sometimes blends insensibly into the lower parts of the compartments, and then perhaps it would not be thought to be a distinct element; but often it is abruptly separated by an overhanging edge (see Pl. 9, fig. 5 b, 9 b; Pl. 20, fig. 1 b; Pl. 25, fig. 1, K') from the lower part, and then the sheath greatly complicates the internal appearance, but not the essential structure of the shell. The sheath acts beautifully, like an internal hoop, in strengthening the shell round the orifice, where it is naturally weaker than at the lower or basal end, where it adheres to the surface of attachment: in the upper part of the shell, moreover, the sutures between the compartments do not go straight through, but owing to the alæ projecting and being overlapped, are extremely oblique; or the joints, in the language of carpenters, may be said to be broken.

There is one other point of structure in the shells of the Balanidæ, more especially of species like Balanus tintinnabulum, which adds to their apparent complexity, namely, that the rim or orifice of the shell formed by the upper ends of the compartments, projects considerably above the opercular valves. In a young Balanus, immediately after the metamorphosis, the operculum is attached by the opercular membrane all round to the summits of the compartments, and there cannot be said to be any orifice to the shell itself, but only an orifice or slit between the opercular valves; but during growth, as the compartments are added to at their basal edges, their upper ends are deserted, and cease to enclose the sack, within which lies the animal's body. Hence the upper ends come to project freely, either quite separately as in some species of Pollicipes, where they cannot be said to form an orifice; or more or less united into a ring so as to form an orifice, as in the different species of Balanidæ. It follows, that to understand the real shape of a Balanus, or rather of the cavity enclosing the animal's body, all that part of the shell which projects above the opercular membrane, may, in imagination, be removed as

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something extraneous, like so many spines; not that I mean to say that these points of shell are dead; on the contrary, they are often porose and penetrated by numerous threads of corium. This upper part of the shell, thus produced so as to form an orifice, no doubt serves to protect the less strong and moveable operculum.

Number and Arrangement of the Compartments.—I have already stated that the shell, in every one of the Balanidæ, consists of eight, six, or four compartments, or of all fused together into a single piece; and that the compartments themselves are all constructed on the three simple patterns of which woodcuts (figs. 1, 2, 3) have been given. They are arranged in a certain definite order. The type arrangement is found amongst the Chthamalinæ, as might have been expected, inasmuch as this sub-family is so closely related to the ancient genera Pollicipes and Scalpellum, whence all the Thoracic Cirripedia may be said to radiate. In Octomeris (fig. 4) the type-arrangement of the com-

Fig. 4.
Octomeris.

Fig 5.
Chthamalus.

Fig 6.
Chamæsipho.

Fig 7.
Balanus.
Fig 8.
Tetraclita.

a, Rostrum; b, Rostro-lateral, c, Lateral, d, Carino-lateral compartment; e, Carina.

Horizontal sections through the Shells of the principal genera of Balanidæ, showing the arrangement of the Compartments. Genera 4, 5, and 6 belong to the Chthamalinæ; 7 and 8 to the Balaninæ.

partments, eight in number, is well shown; the rostrum and carina resemble each other, and have alæ on both sides, and therefore are overlapped on both sides: the

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rostro-lateral compartments have radii on both sides, and therefore overlap the adjoining compartments on both sides; the lateral and carino-lateral compartments have radii on their carinal, and alæ on their rostral sides; and therefore overlap on one side, and are overlapped on the other side. Now the shell of every other sessile Cirripede differs, I believe, from that of Octomeris, only in the fusion together or abortion of some of the eight normal compartments: in one genus, however, Catophragmus, outer whorls of small compartments, arranged like the lower valves in the capitulum of Pollicipes, are superadded. The genus Chthamalus (fig. 5) differs from Octomeris only in the carino-lateral compartments being aborted, (as will presently be discussed), and hence has six compartments. Chamæsipho (fig. 6) differs from Chthamalus only in the rostro-lateral and lateral compartments being fused together; and hence has only four compartments. In Balanus (fig. 7) and the whole sub-family of the Balaninæ, the rostrum is compounded of the true rostrum, as seen in the type Octomeris, and of the two rostro-lateral compartments; hence this compounded rostrum has radii instead of alæ on both sides, and there are only six compartments. Tetraclita (fig. 8) and Elminius differ from Balanus only in having the carino-lateral compartments absent, and probably aborted; hence there are only four compartments. Lastly, in Pyrgoma, all the compartments are blended together into a single piece.

In Pollicipes, the old type-form of the whole order, and in Scalpellum, we have four valves, (answering to the operculum), surrounding the aperture leading into the sack, and the valves below are arranged in successive whorls, with a strong tendency to alternation. For, the rostrum alternates with, that is faces the interval between, the two scuta; the carina alternates with the two terga; and the upper Lateral valves alternate with the scutum and tergum on each side. These four valves, namely, the carina and rostrum, which resemble each other in structure, and the pair of upper latera, which are larger than the other lateral valves, together form the uppermost whorl, or that beneath the scuta and terga. In the next whorl we have the

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rostro- and carino-lateral valves, alternating with those above them; and beneath them there are generally other valves, which decrease in size and display the same tendency to alternation. The valves here just specified, namely, the rostrum, carina, and three pairs of lateral valves, in the Lepadidæ, are so much larger, and are so much more commonly present, than the other valves of the capitulum, that to them alone I affixed special names. Now if amongst sessile Cirripedes we look to that genus, viz., Catophragmus, which comes in its whole structure the nearest to Pollicipes, one of the Lepadidæ, we find (as in fig. 4), firstly, a rostrum and carina resembling each other, and a pair of lateral compartments, larger than the other lateral pairs; these four valves alternating with the opercular valves: and, secondly, we find, but forming part of the same whorl, a pair of rostro-lateral and a pair of carino-lateral compartments, which, just as in Pollicipes, are larger than the exterior and lower valves. These lower little valves, I may remark, decrease in size in the successive whorls, and tend to alternate in position, just as in Pollicipes. Observing these several striking points of correspondence in the valves, (and indeed in the whole structure), of Catophragmus and Pollicipes, one is strongly inclined to suspect that in Catophragmus, and therefore in Octomeris and other sessile Cirripedes, although the rostro- and carino-lateral compartments appear to lie in the same whorl with the rostrum, carina, and large lateral compartments, yet that they really belong, as in Pollicipes and Scalpellum, to a lower whorl. Now if a very young shell of Balanus, immediately after the metamorphosis, be examined, the carino-lateral compartments will be found not to have been developed; they first appear after two or three zones of growth have been added to the other compartments; bearing in mind that in Pollicipes and in Catophragmus the lower whorls are added successively during growth, we find in this fact strong confirmation of the view that the carino-lateral compartments normally belong to a whorl beneath that including the rostrum, carina, and lateral compartments. Whether the rostro-lateral, like the carino-lateral compartments, are developed subsequently to the others, I have had no opportunity of ascertaining, and

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therefore cannot confirm the above analogical conclusion, namely, that they, also, belong to a lower whorl.

In the sub-family Balaninæ, which includes Balanus (woodcut 7), and Tetraclita (woodcut 8), the shell is characterised by not having rostro-lateral compartments, and by the rostrum having radii: now in Pachylasma giganteum, which undoubtedly belongs to the sub-family Chthamalinæ, at a very early age the rostro-lateral compartments become blended with the true rostrum, making a compound rostrum, exactly like the rostrum in the Balaninæ; distinct evidence of a similar fusion is retained throughout life (Pl. 15, fig. 1) in all three species of Chelonobia, which is undoubtedly a member of the Balaninæ. Hence, I think, we may conclude that in all the genera of the Balaninæ the rostro-lateral compartments are probably not aborted, but are blended with a normal rostrum (resembling that in woodcuts, 4, 5, 6), making together a compound rostrum furnished with radii: it must, however, be observed that I could not detect any actual evidence of this fusion in Balanus, even immediately after the metamorphosis. In Chamæsipho (woodcut 6), either the rostro-lateral compartments attain a most unusual breadth, or, as is more probable, they have become confluent with the lateral compartments, which in the Lepadidæ seem to be the most persistent of all the lateral valves. In such genera as Tetraclita and Chthamalus, in which the carino-lateral compartments are absent, they may be fused with the lateral compartments or with the carina; but seeing that they are normally developed later than the other valves, it appears to be the simplest theory to assume, until the contrary be proved, that they are aborted. Finally, the somewhat unexpected conclusion that the shell (not including the operculum) of sessile Cirripedes normally consists of eight valves, four belonging to an upper whorl, and four to a lower whorl, all forced into a single ring, and often more or less fused together; though not strictly proved, is rendered highly probable. I will only further add, that the Basis perhaps represents several whorls of the small valves or scales on the peduncle of Pollicipes, fused together; the comparison of the basis with the calcareous cup, forming the lowest portion of the peduncle in Lithotrya,

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which has been made by some authors, I do not think is very accurate, as the cup in Lithotrya seems to have a special relation to the boring habits of that genus.

Fig. 9.

Basal edge of wall of compartment in Balanus tintinnabulum. a, a, outer lamina; b, b, inner lamina; c, c, longitudinal septa, uniting the inner and outer laminæ, with their ends denticulated.

Structure of the individual compartments.—If the basal margin of a compartment, for instance, of Balanus tintinnabulum, be examined, it appears sufficiently complicated, being composed of an outer and inner lamina, separated by longitudinal septa, which are denticulated at their bases; and the tubes formed by these longitudinal septa are crossed by transverse septa. On the other hand, in some cases, as in the genera Chthamalus and Elminius, each compartment consists of a simple shelly layer. These two extreme states graduate into each other: we have, firstly, on the internal surface, quite irregular points and ridges; these become regular, causing the internal surface to be longitudinally ribbed; then these ribs themselves become finely furrowed on their sides and at their lower ends, producing sharp, minute ridges, the ends of which I have called the denticuli; and, lastly, some of the denticuli on the adjoining longitudinal septa become united into a solid layer, forming the internal lamina of the wall. These denticuli do not generally cover the whole surface of the longitudinal ribs, but leave a portion near the outer lamina of the compartment smooth. The denticulated ends of the longitudinal septa project beyond the basal edge of both the outer and inner laminæ, and enter the mouths of the tubes (where such occur) in the basis, and thus strengthen the shell. The whole of the internal lamina generally is more or less striated longitudinally, thus displaying its origin from the union of the inner edges of the longitudinal septa. I need only further remark that on the internal surface of the outer lamina, between the main longitudinal septa, there are generally (as in the woodcut) smaller longitudinal ridges, which do not reach the inner lamina, and on this account alone are not called septa.

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Tubes are formed by the longitudinal septa, between the outer and inner laminæ. These tubes are almost square, and are occupied by threads of corium, which enter at pores left open between the edge of the compartment and that of the basis on which it rests. The tubes extend high up the compartments; but in the uppermost part they are generally cut off by thin, transverse, calcareous septa, deposited by the ends of the threads of corium; a cancellated structure being thus produced. Or the uppermost part of each tube becomes filled up solidly with compact shelly layers, which are always first thrown down on the side of the tube facing the outside, and thus greatly strengthen the shell: in several instances, as in Balanus perforatus and Tetraclita porosa, in which the disintegration of the upper part of the shell is a necessary element in its growth for the enlargement of the orifice, these filled up tubes become exposed. In Coronula and Tubicinella, the tubes in their upper parts are, I believe, crossed only by transverse membranous septa.

Anomalies and exceptions.—In Tetraclita (Pl. 10, fig. 1 g, 1 h) from the branching of the longitudinal septa, several irregular rows of tubes are formed. In certain varieties of Balanus balanoides (Pl. 7, fig. 2 b), and in B. cariosus (Pl. 7, fig. 3 b), slight branching ridges on the internal surface of the walls, seem to answer to the longitudinal septa, and produce, during the downward growth of the shell, extremely irregular cells, and short tubes. In Balanus vinaceus (Pl. 2, fig. 7 d), the internal lamina, instead of being solid, as in every other species, is left cancellated, and thus betrays, much more plainly than usual, its origin in the united denticuli of the adjoining longitudinal septa. In Balanus porcatus, between the main longitudinal septa, there are (Pl. 6, fig. 4 e) what may be called rudimentary and disconnected longitudinal septa. In Coronula and its allies (Pl. 16, fig. 6, and Pl. 17, fig. 4 c) it is the outer lamina of the compartment which is anomalous; for in the two or three lower zones of growth, it forms only a ledge on each side of the longitudinal septa; which ledges, higher up, become confluent, and so form an ordinary outer lamina. In Coronula, also, the wall of each compartment

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(see transverse section, Pl. 16, figs. 5, 7) is very remarkable from being deeply folded, the folds being on their internal faces firmly calcified together, and on their external faces closely pressed together (often with a neatly serrated suture), so that the whole nature of the shell might be, as has happened, easily quite misunderstood; and the walls be considered as very thick, instead of being, as is really the case, very thin. In Chelonobia (Pl. 15, fig. 1), however, the walls are truly of such great thickness, that the nature of the relative parts might likewise be misunderstood; in this genus the ovarian tubes enter the walls, extending up between the longitudinal septa, or, as they may here be more naturally called, the radiating septa. I will specify a few more peculiarities worthy of remark:—in some species of the sub-genus Acasta, clefts are left, covered only by membrane, on the lines of suture (Pl. 9, figs. 7 a, 8 a), between the compartments, just above the basis; and in other species the basis is perforated by numerous membrane-covered, minute orifices. In Platylepas, each compartment has one deep inward fold (Pl. 17, fig. 1), somewhat analogous to the three folds in Coronula; this fold is produced into an internal mid-rib, supporting and rendering convex the membranous basis; in this genus, also, the rostrum, owing to its mid-rib, is generally thrust a little on one side, and the shell thus rendered asymmetrical. In Chamæsipho scutelliformis the shell is symmetrically perforated (Pl. 19, fig. 4 a) by four apertures. Lastly, in Chthamalus Hembeli and intertextus, after a certain age, the basal edges of the walls become inflected, and continue to grow inwards till they entirely take the place of the true membranous basis.

Radius.—This term, as we have seen, is applied to that side of the compartment, the growth of which is modified, by abutting against and overlapping the adjoining compartment. Hence the structure of the radius is essentially the same with that of the parietal portion of the compartment. When best developed, as in Balanus tintinnabulum, the radius consists of an outer and inner lamina, separated by denticulated septa, extending in horizontal lines parallel to the basis, and is consequently perforated by minute tubes or

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Fig. 10.

Edge of the radius of Balanus tintinnabulum. a, outer lamina; b, inner lamina; c, denticulated septa, uniting the two laminæ.

pores. The tubes become filled up solidly much more commonly than do the parietal tubes; and the inner lamina, in such cases, is hardly distinct from the outer lamina. The denticuli often fail, or are present only on the lower sides of the septa; and very frequently the edge of the radius can only be said to be crenated. Notwithstanding these frequent anomalies, if a series of species and genera be taken, it is certain that there is, as might have been expected, a close relationship in internal structure, between the radii and the parietes. The edge of the radius is received in a slight furrow (generally marked like a seal, with the impression of the denticulated septa) in the opposed compartment: sometimes the outer edge or lid of the recipient furrow, is so broad as to give the false appearance of a radius having been developed, at least in the lower part of the shell, on both sides of the suture. A crest of corium runs into each suture between the edge of the radius and the furrow in the opposed compartment; and when the radius is permeated by pores (as in woodcut 10), threads of corium branch off this crest, and enter the pores. In the lower part of the shell, these crests of corium project from the corium forming and surrounding the sack; but in the upper part of the shell, above the opercular membrane, and therefore above the sack, the corium is produced up each line of suture as a separate ribbon. In proportion as these ribbons extend more or less near to the summit of the shell, so do the edges of the radii continue to be added to, to a greater or less height from the basis; and consequently their summits become less or more oblique.

Peculiarities in the Structure of the Radii.—In some of the species of Tetraclita, in which genus the walls consist of several rows of tubes, the radii are likewise perforated by several rows; and in some of the other species (Pl. 10, fig. 1 h), the edge, or disarticulated surface of the radius, is marked by irregularly branching ridges; and these evidently correspond with the branching septa or ridges of

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the wall. In Chelonobia, the outer lamina of the radius, as well as of its recipient furrow, is of extraordinary thickness; and this lamina, in C. testudinaria (Pl. 14, fig. 1 a, 5, b, and Pl. 15, fig. 1, f), is modelled into sharp transverse ridges and valleys. In the Chthamalinæ, the radii, like the parietes, are simply solid; and apparently in consequence, for the sake of strengthening the sutures, the edges of the radii, and of the recipient furrow in Octomeris (Pl. 20, fig. 3 a) and in Chthamalus dentatus and Hembeli (Pl. 18, fig. 3 b, 5 a), are neatly dentated. In some other species of Chthamalus (Pl. 19, fig. 1 a), the radii present a slight modification of this structure, the sutures being formed by oblique interfolding laminæ. In the radii of Coronula and Tubicinella, there is a peculiarity, in apparent connection with the fact, that in these genera the parietal tubes are not crossed by transverse calcareous septa, namely, that the pores by which the radii are permeated keep unclosed throughout their length, and open into a special longitudinal tube (Pl. 16, fig. 7, d'), which runs along that margin of the wall, whence the radius arises. In Coronula the wall is of extreme thinness, and in conformity so is the true radius; but that the shell might not thus be rendered very weak, complementary or pseudo-radii are developed on their inner sides (Pl. 16, fig. 7, adjoining the true radii A d, C d, and shaded by distant convex lines). Even in the allied genus Xenobalanus, in which the whole shell tends to become rudimentary, traces of these pseudo-radii (Pl. 17, fig. 4 b, d) can be detected. In Coronula, though the radii (Pl. 16, fig. 7, A d, C d) are, by the above special means, rendered thick, and though the alæ also are thick (C a', D a'), yet together they do not equal in thickness the folded walls; and consequently, there is left between the radii and alæ square chambers (v), occupied by the branching ovarian tubes.

Alæ.—These project, generally abruptly, from the sides of the upper part of the compartments; they appear from the first growth of the shell; they are overlapped by the radius and by part of the wall of the adjoining compartment; they are thinner, and have, owing apparently to being overlapped, a very different aspect from the parietal portion; but they do not differ from it in essential nature.

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They are solid, that is, they are never permeated by pores; but their edges are generally crenated, and there is, in some cases, as in Chelonobia, sufficient evidence that these crenations answer to the horizontal septa on the edges of the radii (also often reduced to mere crenations), and consequently, likewise, to the longitudinal septa of the parietes. In Coronula the edge of each ala consists of a medial ridge, sending off denticulated septa on both sides, and is therefore anomalous as compared with the alæ in other genera, but corresponds in structure with the similarly anomalous radius of Coronula. In order to allow of the growth of the edge of the ala, a fine thread of corium runs up the narrow furrow in which the edge is lodged, proceeding from the corium of the sack. In proportion as this thread runs up higher or lower, so are the summits of the alæ rendered, during growth, less or more oblique.

Sheath.—As the compartments overlap each other, the edges of the alæ would have projected, and the inner surface of the orifice of the shell would not have been smooth and rounded, had not that part of each wall, which does not overlie an ala, been thickened so as to allow of the formation of a shoulder or indentation, against which the edge of the ala fits and abuts. The thickened portions, and the alæ themselves, together form the sheath, of which the use seems to be to strengthen, like a broad internal hoop, the upper part of the shell round the orifice, where naturally it is weak. The sheath is composed of successive, fine, shelly layers, which extend, as the shell is added to at the basal margin, lower and lower down on the inner surface of the walls. The lower edge of the sheath either simply projects a little inwards, or more commonly is formed into a sharp depending ridge, as represented in fig. 1, K', Pl. 25. In some species of Pyrgoma (Pl. 13, fig. 2 b), the sheath reaches nearly to the bases of the compartments; and in Chelonobia (Pl. 14, fig. 4 e c e), the inner layer of shell surrounding the sack, which seems to correspond more nearly to the sheath than to the inner lamina of the walls, actually rests on the basal membrane. The opercular membrane is generally, but not invariably, attached only a little way above the lower edge of the sheath: at each exuviation, a new opercular

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membrane is formed, and is attached to the next lower zone of the sheath; the old membrane being cast off, but a circular slip of it is left, investing the last zone. Hence the whole upper part of the sheath above the opercular membrane, comes to be thus invested; and is marked by circular lines, one above the other, caused by the successive exuviations. This investing membrane often supports rows of minute bristles, directed upwards. Generally, a film of shell is deposited, at the period of the formation of each new opercular membrane, on that part of the sheath which lies immediately beneath. This innermost film or thin layer of shell, on the lines of suture between the compartments, breaks joint, at least in some cases, with the underlying shelly layers,—that is, the suture in this last-formed film does not lie exactly over the suture in the subjacent layers of the sheath. In Tubicinella, the sheath extends down close to the basis; and what is unique in this one genus, the opercular membrane, gradually thinning out downwards, closely adheres to the whole inner surface of the shell. In Tubicinella and in Xenobalanus (Pl. 17, fig. 4 b), the sheath separates easily into separate successive rims of shell; and this structure evidently is for the sake of facilitating the breakage of the upper end of the shell, which, as we shall presently see, is necessary to allow of the increase in size of its orifice.

Basis.—This, in several genera and species, is composed of simple membrane, and consists of successive, concentric, circular slips, added round the outside, at each period of growth. In some species of Tetraclita and Balanus the basis is calcareous, but diaphanous, very thin, smooth, or somewhat granulated. In other cases it consists of a single calcareous lamina, either smooth, or with ridges radiating from its centre; it is formed of two laminæ, (as is most usual in Balanus,) separated by radiating septa. These septa, as well as the radiating ridges in the case of the single lamina, are homologous with the longitudinal septa of the parietes. The denticulated ends of the latter enter the mouths of the tubes formed by the radiating septa of the basis: threads of corium pass between the denticuli of the parietal septa, and thus enter the basal tubes. The ends of these threads of

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Fig. 11.

Portion of edge of basis of Balanus tintinnabulum. a, a, outer lamina; b, b, inner or upper lamina; c, c, c, porose or cancellated radiating septa.

corium generally deposit transverse calcareous septa, exactly as within the parietal tubes. When the basis is thick the septa themselves (ccc) between the proper basal tubes, become porose, (or rather cancellated,) and they sometimes expand into a very thick, cancellated layer, separating the outer lamina (a) of the basis from the proper basal tubes, which always lie close under the inner lamina (b). This structure differs only slightly from that seen in the parietes of Tetraclita, in which the branching of the longitudinal parietal septa, produces thick walls, formed of several rows of tubes or pores. With respect to peculiarities in structure of the basis, Balanus lævis offers the most remarkable case; for here, in specimens which have grown crowded together, the whole interior appears sometimes to have become too much elongated or too deep for the animal's body, and consequently the lower part of the deeply-concave basis has been filled up (Pl. 4, fig. 2 a) by thin, irregular, calcareous diaphragms. In elongated specimens, also, of Balanus balanoides, the shell sometimes appears to have grown too long for the animal's body; but in this case the membranous basis becomes extremely convex inwards; it still reaches the basal edges of the parietes all round, but in the middle it is raised high above the surface of attachment; yet sometimes threads of the cementing tissue depend from the middle part to the surface of attachment. In Balanus terebratus (Pl. 8, fig. 2 a, 2 b), and in some species of Acasta, the basis is riddled, as previously stated, by numerous, minute, membrane-covered orifices. In B. declivis the membranous basis is always extremely oblique, owing to the rostral end of the shell being twice as high as the carinal and opposite end.

Regarding the very remarkable means by which the basis of sessile Cirripedes is cemented to the surface of attachment, it will be convenient to defer for a little the description, on account of its necessary length.

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Opercular Valves.—These are situated on each side of the slit or orifice leading into the sack; from their shape, their powers of movement, their separation by flexible membrane from the shell, to which they serve as a lid, they appear at first as if they constituted an element very distinct from the shell itself, but this is not the case. They are, together with the opercular membrane, as essentially as the whole of what is externally visible, a part of the modified carapace, of which they occupy the upper or posterior extremity: from tracing the metamorphoses, or even by comparison of a Balanus with Pollicipes, there can be no doubt of the truth of this conclusion. The opercular valves are four in number,—a pair of scuta and a pair of terga; but the latter in Coronula diadema and reginæ, are either aborted or represented by a mere rudiment; and in Xenobalanus both scuta and terga are quite absent. In several cases, more especially in the genus Pyrgoma (Pl. 13, fig. 1 b), the scutum and tergum on each side are calcified together, so that sometimes not even a trace of the line of junction can be discovered. In most cases the scutum is firmly united, being articulated in a manner presently to be described, to the tergum; but in Coronula, Tubicinella (Pl. 17, fig. 3 c), and Platylepas, the ends of these valves are simply approximated.

Scuta.—These valves are important, inasmuch as the animal's body is attached to them; in Pl. 25, fig. 1, the broken line, surrounding a, b, shows where the body has been cut, in removing the scutum on the near side, the other scutum, S, being left articulated to the tergum, T. In shape the scuta are generally sub-triangular; but in some species of Pyrgoma and in Chelonobia, &c. they are much elongated. The lines of growth are usually prominent; and along the occludent margins the alternate, or sometimes every third or fourth line, is developed into a knob, which produces a serrated edge, serving to lock the two opposed valves together; there is, however, no trace of this structure in Coronula and Tubicinella. In some species of Pyrgoma, a ledge of considerable breadth (Pl. 13, fig. 3 e, &c.) is developed along the occludent margins of the two scuta, as well as of the two terga, giving them an anomalous struc-

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ture. The Terga differ considerably in outline in the different genera and species: their shape approaches more nearly to a triangle than to any other regular form; but there is generally a projection or spur on the basal margin, on the side towards the scutum. In some species of Pyrgoma, the tergum is of so irregular a shape as to defy description. In most cases, a longitudinal depression or furrow runs down the valve, from the apex to the extremity of the spur; and it not rarely happens that the sides of this furrow become folded inwards and almost closed. The spur probably answers to the basal point of the usually sub-rhomboidal tergum in Pollicipes and Scalpellum.* The tips of the terga in some species of Balanus, &c., are specially modified into sharp points or beaks (Pl. 2, fig. 3 b, 3 d), bowed a little inwards, and projecting considerably above the tips of the scuta; this is effected by the medial, uppermost part of the valve being internally thickened and hardened, and then, by the disintegration of the two margins and the external surface, the internal modified portion becomes exposed. The whole valve, also, at least in such cases as in Balanus psittacus, appears to be forced slowly upwards in the articular furrow of the scutum. I am assured, by a competent observer, that the beaks of the terga in B. porcatus can give an object placed within the orifice of the shell a sharp tap.

The scutum and tergum, with the few exceptions above stated, are articulated together at a large or open angle. The articulation (see Pl. 11, fig. 5 b, c, d, and fig. 6 b, c) is effected by the margin of the tergum being a little inflected, and lodged in a furrow in the margin of the scutum. This

* In comparing the Tergum of one of the Balanidæ with that of a typical member of the Lepadidæ, for instance, that of Balanus with that of Pollicipes, apex corresponds with apex: the extremity of the spur in Balanus corresponds with the basal point of the whole valve in Pollicipes: the scutal margin, (which in Balanus homologically extends down to the extremity of the spur), corresponds with the scutal margin of Pollicipes: the carinal margin in Balanus corresponds with the upper carinal margin in Pollicipes: the basal margin of Balanus on the carinal side of the spur, corresponds with the lower carinal margin in Pollicipes: lastly, (and this is the chief difference), in Balanus there is no appreciable occludent margin, the apex of the valve being brought close to the upper angle of the scutal margin; in Chthamalus, however, there is yet left some remnant of an occludent margin,—which margin in Pollicipes is conspicuous.

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furrow in the scutum has its further border generally prominent and often reflexed or curved over; I have called it the articular ridge; it, also, is lodged in a furrow in the upper part of the tergum, which again is bordered by a ridge, viz., the articular tergal ridge. So that in both scutum and tergum there is an articular furrow, bordered in each case, on one side by the margin of the valve, and on the other side by the so-called articular ridge. In Chelonobia (Pl. 14, fig. 1 b) the articular ridge of the scutum is horny. When, as often happens, the scuta and terga have been much worn, the manner of their articulation (Pl. 18, fig. 1 a) is pretty well shown even from the outside; in this case their external appearance is very different from what it is in those individuals fig. 1 c) of the same species, which have not suffered disintegration. This articulation of the scuta and terga is prefigured amongst the Lepadidæ, in Pollicipes mitella, and in Lithotrya.

The scuta are brought together by a short, strong, straight, adductor muscle (Pl. 25, fig. 1 a); its attachment leaves (with very few exceptions, as in Tubicinella) a rounded impression, or even pit, on the under side of the valve in its upper part. This pit is frequently bounded, on its lower side, by a sharp ridge, which, though not in actual connexion with the adductor muscle, I have, for convenience sake, called the adductor ridge; it serves apparently to give support to the animal's body; in some few cases (as in B. psittacus, Pl. 2, fig. 3 e) it is confluent at its upper end with the articular ridge, and converts the whole basi-tergal corner of the valve into a deep cavity. In some of the species of Pyrgoma (Pl. 12, fig. 5 c, 7 b), and in some varieties of Creusia, this adductor ridge is enormously developed, so as to depend far beneath the true basal margin, or that to which the opercular membrane is attached. At the basi-tergal corner of the valve, there is generally a small pit or impression, and sometimes distinct crests, for the attachment of the lateral depressor muscle. At the rostral end there is, also, a small cavity formed by the overfolding of the occludent margin (rarely furnished with crests) for the attachment of the rostral depressor muscle. In the Terga, at the basi-carinal corner, there are usually crests, though

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sometimes feebly developed, for the attachment of the tergal depressor muscle. But in Chelonobia, Coronula, Tubicinella, Platylepas, and in some other cases, there are no crests. The crests, when well developed, are furnished with rectangular sub-crests or denticuli on both sides; in fact they resemble, and are probably homologous with, the denticulated ribs or septa in the parietes, radii, and basis. Altogether the scuta and terga are attached, as far as muscles are concerned, to the shell and sack, by three longitudinal pairs.

Growth of the whole Shell, and its Microscopical Structure.—The opercular valves are added to along their basal margins alone;* the animal's body, together with the several muscles, becoming attached at each period of growth lower and lower down to the valves; this no doubt is effected by the absorption of the upper surfaces of the muscles, and the formation of new fasciæ on their lower surfaces. The opercular membrane, which, though thin and flexible, forms part of the general outer surface of the animal as much as does any portion of the rigid shell, with which indeed it is strictly homologous, is periodically moulted, together with the integuments of the whole included animal. The new opercular membrane is of course each time formed a little larger than the old one. In Coronula and Tubicinella, however, several successive opercular membranes are preserved one over the other, and the outside membrane gradually disintegrates; in these cases the undermost opercular membrane is formed wrinkled and considerably too large, so as to allow of being stretched, before it is finally cast off. In Tubicinella, the opercular membrane runs down, adhering to the inner surface of the shell, to nearly the basis, and hence during the diametric growth of the shell, it is longitudinally split, and is repaired by slips of new membrane, which resemble the radii in form and in direction of the lines of growth.

The basis is added to only round the circumference and

* In some species of Pyrgoma, the ledge (limbus occludens) which is added along the occludent margin of both scuta and terga, and in some species of Balanus a narrow rim, or slight protuberance which is added along the carinal margin of the terga, offer unimportant exceptions to the rule, that the opercular valves grow only at their basal margins.

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hence increases in diameter, and, when concave, in depth. The compartments grow at their basal margins, where they are in contact with the basis; hence the shell is added to in height, and, owing to the outward inclination of the compartments, also, in basal diameter; but the compartments likewise, in most cases, grow along both lateral margins, that is, on the edges of the radii and alæ; and hence the upper part of the shell, also, increases in diameter. The orifice of the shell, moreover, thus becomes enlarged. In some cases the shell is destitute of radii, only sutures being present, that is, the compartments do not grow laterally; and sometimes, as in the whole genus Pyrgoma, there are not even sutures, the compartments having been fused together: in both these cases, the shell can increase in diameter only at the base; and the orifice, it might have been thought, would necessarily have remained, to the destruction of the animal, of the same minute size, as when first formed after the metamorphosis: this certainly would have been the case had not the upper ends of the compartments, surrounding and forming the orifice, been nicely adapted always to yield, in a certain limited degree, to the disintegrating influences to which every shell is exposed, but which most Cirripedes can resist; and the disintegration of the narrow end of a conical tube, of course increases the diameter of its orifice. In Tubicinella, in which the shell is furnished with narrow radii, and does increase in diameter from top to bottom, the increase is not sufficient in proportion to the continued elongation of the shell; to compensate for this, the orifice is enlarged at short intervals by the breakage of the upper end of the shell, for which purpose (as explained under the genus) it is evidently constructed. Hence we see that, in certain Cirripedes, decay or disintegration, and breakage, are necessary elements in their growth! It is a remarkable fact, which I cannot explain, that in some species in which the orifice of the shell is usually increased by disintegration, if individuals are so situated that they are not exposed to sufficiently energetic disintegrating influences, as may be inferred from the well-preserved condition of the whole surface of the shell, then the radii become developed, and the orifice is increased in size by the diametric growth of

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the upper part of the shell: I have seen instances of this in Tetraclita porosa, and purpurascens, and in Balanus perforatus: it appeared, but of course erroneously, as if the lateral growth of the compartments had been subjected to the will of the animal.

Considering the strength of the shell of sessile Cirripedes, the separation of their compartments one from another and from the basis, during growth, has justly been thought a surprising circumstance. In most Chthamalinæ and in some species of Balanus, however, if the shell be boiled in caustic potash, the compartments fall apart with a touch; this shows that their union is due to animal and probably to organised matter, and the growth of such matter between the opposed edges of the compartments, and their consequent gradual separation, offers no particular difficulty. But in many Balani, boiling in potash for hours does not seem even to weaken, in the least degree, the sutures, which are wonderfully strong—the shell often breaking rather than yield on these lines; if, however, the shell be dissolved in acid, the animalised tissue which is left easily separates on the lines of suture, and if this tissue be boiled in potash, the remnants of the compartments fall quite separate. These facts seem to me to show, that the compartments in such cases are joined along the lines of suture by tissue, which must be in a calcified state, but which, nevertheless, continues to grow by intersusception; in other words, I believe that the tips of the complicated ridges and points interlocking on the lines of suture, are not separated from each other by films of corium or simple animal matter, but are actually united by corium in a calcified, yet still growing condition.

In ordinary Crustaceans, the growth is periodical and sudden; a new and larger carapace, for instance, is formed under the old one, and after the exuviation of the latter, the new one soon hardens, and does not subsequently increase in size; so it is in the case of Cirripedes, with the membranes of the body, and even with certain parts, as the opercular membrane, of the external covering. But a Cirripede cannot, like a crab, crawl into some crevice and remain protected till its shell becomes hardened; hence, probably, it is that

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the shell is never* wholly moulted. Even if the margins of the opposed compartments and of the basis were to grow rapidly, the shell would necessarily be much weakened on the lines of suture, and unable to withstand the heavy breakers, to which so many species of sessile Cirripedes are exposed. On the other hand, although the margins are thus compelled to grow slowly, they do not grow continuously, as may be seen in the zones of increment on all the valves, corresponding, I believe, with the periods of exuviation of the membranes of the body. A layer of shell, often very thin, seems to be generally deposited over the whole internal surface of the several valves, at the same time that the marginal zones are added; so that the only essential difference in the growth of the external covering, in Cirripedes as compared with ordinary Crustaceans, is that the old shell is not cast off, but adheres to the outside of the new shell, and that the margins are added to (in certain definite directions) slowly yet not continuously, instead of the whole being formed at a single period.

If, now, a section of one of the shelly zones of growth be carefully examined, it can in some cases be distinctly seen to be formed of successive, excessively fine laminæ; but the animalised tissue (which differs much in amount in different Cirripedes) left after the shell has been dissolved in acid, exhibits, in most cases, neither laminæ nor any other structure whatever. The shell seems to be the actual pulpy corium, or true skin, in a calcified condition, but generally with its cellular structure modified and much reduced: I have taken a bit of recently-formed shell of Tetraclita and of Coronula, with the corium still adherent to its under surface, and after dissolution in acid, I could not distinguish the part, which had just before existed as shell, from the corium itself. In the case of Coronula, immediately

* In the genus Alcippe, and in Cryptophialus, the whole of the external membranes are moulted, excepting the surface of attachment; but then these Cirripedes live in cavities which they form for themselves, and are thus protected. In Lithotrya the membrane of the peduncle, with its little valves or scales, is moulted, but here, again, this very part is protected by the tubular cavity, which the animal forms and inhabits. Neither of these three genera belong to the Balanidæ, or sessile Cirripedes, which we are now more especially describing.

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prior to the period of moulting and growth, I found the unaltered corium so charged, as to effervesce, with carbonate of lime, either in a state of dissolution, or in granules too minute to be visible under the highest powers.

The sutures between the several compartments and the basis are covered by thin membrane, which is continually splitting during the growth of the opposed edges of the underlying shell; but previously to each splitting, a new slip of membrane is, I believe, already formed under the old one; so that the corium is not even momentarily exposed. Owing to this manner of growth, the slips of membrane consist of successive rims united together; in most cases, these soon become abraded from the older parts of the shell, but are sometimes preserved. The last-formed slip of membrane over a suture is homologous with the opercular membrane; and both are strictly analogous with the ring of flexible membrane, forming the joint of the leg of a crab. In the latter case, the flexible membrane and hardened crust are both moulted together: in the opercular membrane, there is a double line of splitting, one close round the opercular valves, and the other at the basal edge of the sheath, and the intermediate portion is moulted, but with a zone of membrane left adherent to the non-moulted valves and sheath: lastly, in the slips of membrane covering the sutures, there is only a single line of splitting, and no portion, I believe, is moulted; the rims of membrane on each side remaining adherent on the compartments and basis, until worn away.

The opercular membrane, when closely examined, exhibits no structure, except that it can sometimes be plainly seen to be composed of successive, numerous, excessively thin laminæ. Occasionally, however, it presents the false appearance of being permeated by parallel and anastomosing vessels: this appearance is due to one or more of the component laminæ having been wrinkled before a succeeding lamina was thrown down and attached to its under side. If a small piece of an opercular valve of Tubicinella, with the opercular membrane adhering to it, and with the corium under both, be dissolved in acid, it may be clearly made out that the corium under the valve has gone on

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being converted into shell, whereas under the opercular membrane it has been converted and condensed into fine constituent laminæ of chitine. Inasmuch as the successive layers of shell, during each period of growth, go on encroaching on those of the membrane, the line of junction between the shell and chitine becomes oblique or bevelled. The membrane on this bevelled line of junction assumes a slightly different aspect to what it has elsewhere; it becomes yellowish or brown, thicker and very much tougher. In many genera it is also furnished with a row of small bristles. At the period of exuviation the opercular membrane separates just outside this modified portion, leaving the latter adherent, as a rim or slip, on the valves. If, however, the opercular membrane be rudely torn off before its proper period of exuviation, it carries with it the as yet continuous, but already modified, slip. A slightly indented line may sometimes be traced before the period of exuviation, showing where the separation will take place: what produces this line I know not. The coloured, thickened, and modified slips of opercular membrane, which are thus retained adhering to the valves, and which together form an investing membrane, have been considered by most authors as the epidermis; but they have no more right to be thus called than has any other part of the opercular membrane. Exactly similar slips of membrane are left investing the sheath. So, again, the membrane which, when well preserved, invests the walls of the shell, is made up, as already stated, of successively adherent slips, which originally covered the lines of suture.*

The little bristles above alluded to, which arise from the

* In the case of Coronula there is a peculiarity, described in the last section of this Introduction, (under the head of Cementing Apparatus), namely, that the two or three last-formed, exterior zones of the Basal membrane continue for a period to increase in width; being, as I believe, dragged one from over the other, with fresh laminæ of membrane continually thrown down. In this same genus, and in Tubicinella, the walls of the shell are invested by membrane, which is doubled inwards under their basal edges; and as the latter grow, the investing parietal membrane splits and separates from the basal membrane, and is pulled outwards and downwards. This inflected, often broad border of membrane, seems to me more strictly comparable with the opercular membrane, than with those narrow, thickened rims of yellowish membrane which in other Cirripedes cover the suture between the basal edges of the walls and the basis.

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slips of membrane left adherent on the opercular valves, sheath, and walls, stand in rows; a row corresponding to each period of exuviation of the opercular membrane. The bristles are generally largest on the opercular valves and sheath; in Balanus tintinnabulum, they are from 1 to 2/1000ths of an inch in length, but they are longer in some other species. I may here mention, as showing the connexion of these bristles with the opercular membrane, that similar bristles occur in B. perforatus, scattered over the surface of that membrane, and are necessarily moulted with it. In the imbedded genera Coronula and Tubicinella, none of these bristles exist. When a portion of valve or shell, furnished with bristles, is dissolved in acid, tough, sinuous, and apparently hollow, threads are seen to run from their bulb-like bases, into and up the corresponding layer, which, before dissolution, existed as shell; and they terminate internally in very fine points, which I believe are united to the underlying corium. These threads, or tubuli,* as I have called them in my volume on the Lepadidæ, are, in Tetraclita porosa, about 1/5000ths of an inch in diameter, but only half that size in B. tintinnabulum. On parts of the shell where there are no bristles, similar tubuli penetrate the shelly layers, and come to the surface. The tubuli running to the lowest and last-formed row of bristles, just after a period of exuviation, are so delicate as hardly, or not at all, to be distinguished; in the row above, they are plain and longer, and for the next two or three upper rows they are, in some cases, as in Tetraclita porosa, longer and longer, having been added to during each successive thickening of the valve. These tubuli consist of chitine, and no doubt first existed as threads of corium; they are so tough that they must serve to strengthen the successive layers of shell, but I imagine their chief function is to keep up the vitality of the newly-formed layers of shell. May we not, also, venture to suppose that by their means, some degree of sensibility is given to the bristles?

* I regret that I have used this term "tubuli"; for the threads thus designated, I believe, are not the same with the tubuli of Dr. Carpenter, which are not left after dissolution in acid. I have seen tubuli, as called by me, in the shell from the leg of a crab, after having been placed in acid.

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I need only further remark, that in some species of Balanus and of Chthamalus, the under side of the shell is penetrated by irregular pores, large enough to be visible to the naked eye, into which threads of corium penetrate; but these can hardly be said to appertain to the microscopical structure; and are more nearly related to those pores and furrows, formed by the greater or less development of the longitudinal septa, and in which the threads of corium deposit, or rather become changed into, transverse septa, or solid shelly matter, as previously described.

Sack; muscles of, &c.

In the pupa, the thorax, as we shall hereafter more fully see, is continuous with, and opens into the large anterior end or front part of the head; but during the metamorphosis (Pl. 30, fig. 2), the thorax of the Cirripede becomes, owing to the almost transverse position occupied by the young animal within the pupa, to a great extent internally separated from the anterior end,—which anterior end forms, as we know, either the peduncle or the basis. Hence it comes to pass that the body or thorax (Pl. 25, fig. 1) is lodged within a sack (f) within the shell. The chitine membrane lining this sack is excessively thin and transparent, but less so in Xenobalanus and Tubicinella; it is obviously continuous with that investing the body of the animal; it is also essentially continuous with the opercular valves and membrane, and consequently with the whole shell. It is periodically moulted. It is lined by corium, as is likewise the surrounding shell; hence the corium is double round the sack, as indeed might have been expected from the shell and opercular valves (at least their upper parts) being formed by the prolongation, as is obvious in the pupa, of the posterior edges of the carapace. Between the two folds of corium, which are united together by transverse ligamentous fibres, branching out at both extremities, like the roots and branches of a tree, we have the longitudinal muscles, which go to the opercular valves; and likewise a layer-like mass of branching ovarian tubes (Pl. 25, fig. 1 g): the ovarian tubes, however, are often confined to the base

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of the sack. In Xenobalanus, the two folds of corium are united by longitudinal membranous septa, making a series of quite peculiar, square tubes.

The above-mentioned muscles are attached at their upper ends to the opercular valves, and at their lower ends to the basis. There are, in fact, three pairs, but the pair attached to the basi-carinal angles of the two terga (Pl. 25, fig. 1 i), are almost invariably confluent, forming one great bundle; the second pair is attached to the lateral or basi-tergal corners of the two scuta, and are hidden in the figure; the third pair (h) is attached also to the scuta, to their rostral angles. These muscles can only act as depressors; they are often extremely powerful; they belong to the voluntary class, for they are transversely striped. By their action, the opercular valves are capable of varied slight movements, within the limit allowed by the width of the flexible opercular membrane. By the action of the lateral scutal depressores, the orifice leading into the sack is opened, the movement being generally aided by the protrusion of the cirri. By the sudden contraction of the rostral scutal depressores, the blows which are sometimes given by the beaked terga at the opposite end of the operculum, are probably effected. By the contraction of all three pairs of muscles, the opercular valves are held down with quite surprising force. The valves can be raised only by the action of the animal's body against the basis.

In Coronula these muscles are more spread out, and do not extend down to the basis; their lower portions, as is likewise the case in Tubicinella, do not exhibit transverse striæ, and hence tend to pass either into the involuntary class, or into ligament. This condition of the muscles, in the above two genera, accords with the little-developed state of their opercular valves. In Xenobalanus, there is no longer any evidence of the muscles being collected into five or six bundles, for they are thinly and almost uniformly spread out, and show in no part transverse striæ. I may add that in much elongated specimens of Balanus balanoides, these muscles become in their lower part ligamentous, and destitute of striæ.

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Branchiæ.

In the Balaninæ, a pair of Branchiæ is always present: they lie on each side, in a somewhat curved position, in the angle between the sides of the shell and the basis. In Pl. 25, fig. 1, they are exactly covered, on the further side, by the body of the animal. They are attached near each other at the carinal end of the sack in a vertical line, and likewise on each side in a transverse line, extending from close beneath the spur of the tergum towards the point of attachment of the body to the scutum. In Balanus, as in the figure (Pl. 25, fig. 3) of B. tintinnabulum, each branchia consists of a medial fold of skin, a little curved conformably with the sack, and slightly tapering towards its rostral and free extremity; but this fold is almost hidden by the vertical subfolds or membranous ridges, themselves plicated and sub-plicated, which project on both sides: these vertical folds are free at their tips: at their lower attached ends, they are thickest. On the side nearest the wall of the shell, the whole branchia has a bilobed appearance, owing to a very deep indentation caused by the projection of the scutal lateral depressor muscle; the sub-folds on this side are also more plicated. The branchia essentially is an inward plicated fold of the membranes of the sack; for its outer, very thin tunic is continuous with and moulted with that lining the sack; and within it we have two layers of delicate, pulpy, transparent corium, united together (as is best seen in Coronula) by ligamentous fibres, branched at their two ends, all exactly as in the corium surrounding the sack. There are here no distinct vessels, any more than in other parts of the body, but a fluid could easily circulate in the interspaces of the corium. From the large size of this organ, and its simplicity of internal structure, being adapted exclusively to expose a great surface of skin to the water, I do not doubt that it has been correctly considered as a respiratory organ. By the voluntary movements of the opercular valves (i. e. part of the carapace) the water is constantly being pumped in and out of the sack; the movement, indeed, may be

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almost compared to the heaving of a man's chest. Moreover, the branchiæ on each side are attached so closely to the spur of the tergum, that each time the latter is moved, the whole branchia must, I think, be agitated, and the folds opened, as by the action of a lever.

In our two commonest, tidal, sessile Cirripedes, viz. Balanus balanoides and Chthamalus stellatus, I have observed that, when left uncovered by water, they kept the orifice of their operculums a little open, with a bubble of air within their sacks, so that the orifice was in fact closed by a thin septum of water, with air beneath; when disturbed, they closed their operculums with force, and expelled the bubble of air with a clicking noise, which has been noticed by Dr. Coldstream,* and has been thought to be made by the movement of the operculum itself. Bal. crenatus, a deepwater species, when out of water, keeps its operculum closed.

In Coronula, Platylepas, Tubicinella, and Xenobalanus, each branchia† consists of two unequal folds, both plicated on both sides: in the two latter genera, they extend far down the deep and elongated sacks, and hence the area of surface altogether gained is extremely great. In most of the species of Chthamalus, the branchia consist of a small fillet barely plicated: in the allied Chamæsipho columna, they are rudimentary, forming a smooth little pouch only 1/100th of an inch in length: in Chthamalus scabrosus they are quite aborted, being perhaps represented by a slight hairy ridge; but in Chthamalus dentatus, and therefore within the limits of the same genus, the branchiæ (and this seems to me a singular fact) are large, each being composed of two plicated folds, as in Coronula. Tapering filaments situated near the bases of the cirri, such as those occurring in several species of the Lepadidæ, are not found in any sessile Cirripede; but I have observed nearly similar filaments, projecting upwards and inwards at the base of the sack, in several species of Balanus and in Coronula; those which I

* 'Encyclopædia of Anatomy and Physiology;' article Cirrhopoda.

† Burmeister has given a good figure (Tab. 2, fig. 10) of the branchiæ of Coronula, (but the two folds are shaded too unequally), in his 'Beiträge zur Naturgeschichte der Rankenfüsser.'

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examined were simply occupied by delicate corium, and no doubt must aid in exposing a greater surface of corium to the circumambient water.

In my former volume on the Lepadidæ, I have described the ovigerous fræna occurring on the two sides of the sack, to which the ovigerous lamellæ are attached by a peculiar glandular secretion: in the Balanidæ there are no ovigerous fræna, but the branchiæ just described are identical with the fræna in essential structure and in position; differing only in being placed a little nearer to the carinal end of the sack, and in being generally (but not always) larger and more plicated: seeing this, and that in Alcippe lampas, and in some species of Pollicipes,—the genus which comes nearest to the Balanidæ,—the ovigerous fræna are large and are destitute of glands, and have therefore lost their normal function of supporting the ovigerous lamellæ, I can hardly doubt that the branchiæ in the Balanidæ are the ovigerous fræna of the Lepadidæ in a modified condition; a transformation of function not greater than that of the swimming bladder of a fish into the lungs of the higher Vertebrata.*

Parts of the body included within the shell or carapace.

These parts (Pl. 25, fig. 1) consist of the prominent mouth, and of the thorax (c'), with its largely developed portion, called the prosoma (c), and with its appendages. The abdomen is quite rudimentary, being represented merely by a small portion of membrane surrounding the anus, and sometimes inserted like a wedge between the inwardly inflected posterior thoracic segments; in only two genera (Catophragmus and Pachylasma), its nature is rendered somewhat plainer by supporting caudal appendages. The probosciformed penis lies folded under the thorax; and I believe (from what is seen in the anomalous genus Proteolepas), that it normally arises from the ventral

* There is, I conceive, no foundation for the belief of some authors that the branchiæ of the Balanidæ are in any way connected with the ovaria.

5                  

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surface of the terminal point of the rudimentary abdomen.* The thorax is laterally compressed, the ventral surface being very narrow, with the bases of the cirri placed closely together. It consists, in appearance, of two very different portions; one a soft, more or less rounded bag, which I have called the prosoma; and the other, which supports the five posterior pairs of cirri, is narrower, invested with stiffer membrane, and is more or less distinctly composed of five segments. These segments (Pl. 26, fig. 8) on their dorsal and dorso-lateral surfaces, are generally driven like wedges one into the other, with their points directed anteriorly: on the ventral surface the articulations are transverse. The prolongation (e) of the thin membrane (a) surrounding the anus (b), that is, the rudiment of the abdomen, which sometimes carries caudal appendages, almost divides (in appearance, whether really I know not) the hindermost thoracic segment along the medio-dorsal line, into two parts. I have given the above drawing of these segments, but with the dorsal surface much flattened, in Coronula diadema; in most species of Balanus, however, the wedges formed by one segment being driven into another, are much sharper; on the other hand, in Xenobalanus they are nearly straight and transverse. The three posterior segments are always the most distinct; the two next segments are also distinct laterally, but along the dorsal surface they become, excepting in Xenobalanus and some few other cases, completely confluent. The greater distinctness of the posterior segments is conformable to what takes place in the higher Crustacea. The articulations between the segments are folded inwards, and are formed of thin membrane, which in some cases, as in Coronula diadema, forms a marked contrast with the much thicker, stiffer, and yellowish membrane of the segments themselves; in Balanus tintinnabulum, how-

* Von Siebold and Stannius, in their 'Anatomie Comparée,' tom. i, p. 473, and p. 440, foot-note), consider the articulated probosciformed penis as an elongated abdomen; a view which, at the commencement of my examination, I was tempted to admit; but the position of the caudal appendages on the dorsal basis of the penis, suffice, I think, to show that this view is not correct; for these caudal appendages evidently correspond with those borne on the very extremity of the abdomen in the pupa. Nor, indeed, does the position of the anus accord well with such a view.

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ever, the whole membrane of the five thoracic segments is very thin, excepting small wedge-shaped portions along the medio-dorsal line. The infolded articulations between the segments supporting the three anterior pairs of cirri (at least in the Balaninæ), are much wider than those between the three posterior segments; the former segments, with their cirri, being consequently capable of being moved further apart from each other. Could there have been any doubt as to the distinctness and reality of the five thoracic segments, it would have been set aside by the arrangement of the muscles attached to them, as will presently be described. I need only add, that in many genera there are shield-like swellings at the exterior bases of the pedicels of the posterior cirri, which I for some time thought were the epimeral elements of the thoracic segments; but I now believe them to be parts of the pedicels of the cirri. The basi-exterior margin, moreover, of the pedicel of the third pair of cirri, in many species of the Balaninæ (Pl. 25, fig. 1), is produced as a plate, thickly fringed with fine hairs, half across the dorsal surface of the thorax; serving, apparently, as a brush to clean the sack, or to prevent the ingress of any intruding substance.

The soft, rounded, bag-like portion of the body, which I have called the prosoma, is usually separated by a notch from the five posterior thoracic segments; at its upper end it may be said to carry the mouth and first pair of cirri. The prosoma includes the main part of the stomach and the broad ends of the vesiculæ seminales. It is always clothed by very thin membrane, which in Chthamalus dentatus, is hairy. In Tubicinella and Xenobalanus, the prosoma is much elongated, being produced far down the deep sack. That the prosoma is mainly formed by a great development of that segment (homologically the second thoracic segment) which carries the first pair of cirri, is certain, and I should not have hesitated to have said that it was exclusively so formed, had not the first thoracic segment in the anomalous genus Cryptophialus been developed as a distinct and free segment, not attached to the carapace; showing that possibly in other Cirripedes, the dorsal half of this first thoracic segment may be concerned in the formation of the free prosoma.

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Attachment of the Body to the Shell. Muscular System.

The prosoma which carries the posterior thoracic segments, and in appearance the mouth, is the only part of the body which is attached to the general covering (Pl. 25, fig. 1), namely, to the opercular valves. Except through the continuity of the lining membranes of the sack, the body lies free within the walls of the shell. The area of attachment (shown by a sinuous broken line round a and b) extends from about the middle of the two scuta down to their basal margins. As these valves lie obliquely across the orifice of the shell, the animal's body comes to be suspended almost in the middle of the sack. The two scuta, as we have seen, have the power of opening and shutting a little; and are brought together by the adductor scutorum muscle (a), which is generally very powerful. The body is attached to these valves, round and beneath the adductor, so as to hide it until one of the valves be removed. The attachment is chiefly effected by three pairs of widely expanded, superficial muscles, two pairs of which are spread over the flanks of the prosoma, and the third pair over its rounded (properly dorsal) surface, which lies close to the rostral compartment (A, fig. 1) of the shell. I should have stated, that my chief examination of the attachment of the body to the scutal valves, has been made on Coronula balænaris, and less closely on Balanus tintinnabulum. Within these three pairs of superficial muscles, there are (besides the adductor) no less than five other pairs; of these one long pair is attached at one end to the basal margin of the labrum (e), and at the other end, to the under side, near to the basal margin of the scuta: two other, shorter, parallel pairs of muscles are attached at one end to the interspace of membrane between the basal edge of the labrum and the adductor scutorum muscle, and at the other end, to the under side of the scuta, above the attachment of the first pair: the fourth and shortest pair curls close under the adductor, and is there attached at both ends beneath it. The action of these four pairs of muscles must be to draw back, from the orifice of the shell, the mouth, and that inter-

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space of body between the basal margin of the labrum and the adductor muscle. This movement I saw in living specimens. The last and fifth pair of muscles is small, but of considerable length; it is a diverging pair, attached at the converging end, above and exteriorly to the adductor muscle; and at the diverging end, low down on the under side of the scuta; I am very doubtful regarding the function of this pair. Altogether we have seen that round and within the fleshy pedicel, by which the body is attached to the scuta, there are no less than eight pairs of muscles. The central space between these muscles is hollow, and here many lacunal channels seem to converge. These muscles receive nerves from the supra-œsophageal ganglions. The interspace above alluded to, between the basal edge of the labrum and the adductor scutorum muscle, occupies a very different position according as the animal's body is protruded as far as it can be, or is retracted. It is homologically part of the third cephalic segment; and consequently the mouth ought to have stood posteriorly (i. e. above, in the position figured in Pl. 25, fig. 1) to this interspace; yet, in fact, when the animal is retracted within its shell, the mouth usually lies almost directly beneath this interspace and the adductor scutorum muscle.

Besides these muscles of attachment, the prosoma is furnished with several other muscles. There are superficial muscles running up towards the basal margin of the sides of the mouth; and other deeper muscles, to which, I presume, the movements of the mouth, as a whole, are due. The muscles moving the gnathites do not, as far as I could make out, extend beneath the basal edge of the mouth. There are, also, powerful muscles giving movement to the basal segments of the pedicel of the first pair of cirri. Again, there are superficial muscles running to the next succeeding thoracic segment; the anterior ends of which are separated by a clear interspace from the lower ends of the above-described superficial muscles, by which the prosoma is attached to the scuta. On each flank, moreover, but more deeply imbedded, are the long flexor and extensor muscles, presently to be described, running to the five posterior thoracic segments. The last muscle which I need here

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mention, is a deep-seated diverging pair, attached near the upper end of the stomach, on its ventral surface, and diverging from this point to the sides of the prosoma high up beneath the mouth. The probable action of this pair, as well as of the three superficial pairs of muscles by which the body is attached to the scuta, is to draw up the whole prosoma towards or from the orifice; and likewise to contract it firmly, so as to serve as a fulcrum for the movements of the five posterior thoracic segments, together with the cirri, which they carry.

The muscles of these five thoracic segments are numerous and powerful; they are also complicated, chiefly owing to the segments on their dorsal and dorso-lateral surfaces being driven, like wedges, one into the other. As far as I could make out, there are on each side three, superficial, dorso-lateral and lateral muscles (generally, if not always, destitute of striæ), which do not cross the articulations, but extend merely from articulation to articulation; and of which the function can be only to contract each separate segment, and consequently to open out the intermediate infolded articulations; the effect of this would be to separate slightly the cirri from each other,—more especially those borne on the two or three anterior segments, between which the infolded articulations are deeper or broader. There are other more deeply imbedded, powerful, long, dorso-lateral extensor, and ventri-lateral flexor muscles, attached at one end within the flanks of the prosoma, and at the other end to the successive segments of the thorax. The action of the former is to straighten and stretch out the thorax; of the latter, or ventri-lateral muscles, to retract it. In tracing these muscles, a fascia could be seen to become attached to a segment, and then this same fascia would run on to the next succeeding segment: the effect of this must be, that each segment can be retracted and protracted either from the prosoma as a fulcrum, or from the antecedent segment as a fulcrum: we have, also, seen that each segment can, by the agency of the superficial, non-striated muscles, contract itself. Hence these thoracic segments are capable of diverse movements, as was very evident when the shell of a living specimen was opened. By one movement in

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common, the whole five posterior segments could be drawn back, so as to become even partly imbedded in the prosoma: lateral, twisting or wriggling movements were also quite distinct: the three posterior segments seemed to be capable of less independent movements than the anterior segments; and I observed that the more powerful flexor and extensor muscles did not run into these three posterior segments. The cirri, of course, partake of the movements of the thorax; and in watching, in an uninjured specimen, the alternate, protruding, gracefully sweeping and retracting movements of the posterior pairs of cirri, it was evident that the thorax was the chief agent in their movement. Besides the muscles now mentioned, there are some immediately to be noticed, which extend from within the thoracic segments to within the pedicels of the cirri.

Movements and Muscles of the Cirri.—Although the cirri have not been described, it will be most convenient here to treat shortly of their muscles. Each cirrus consists of a pedicel, having a long basal and a short upper segment, supporting two multiarticulate rami. The lower segment of the pedicel can be drawn forward by an adductor muscle, attached low down within this segment, and crossing at right angles (at least in the case of the anterior cirri) the corresponding muscle of the opposed cirrus, on the central, ventral surface of the thorax. This segment can also be drawn back by a muscle springing from the dorso-lateral surface of the thorax, and running only a little way within the segment: I am far from sure that the lower segment does not possess other muscles. The short upper segment of the pedicel can be moved backwards and forwards, as I saw in living specimens, independently of the lower segment; this movement being best seen in the anterior cirri, which are much more often moved independently of each other than are the posterior cirri. The rami are capable, I believe, of being moved backwards and forwards as a whole, by the movement of the few lower segments, which are generally more or less confluent. They can, also, be curled up and uncurled by the combined movement of each separate segment. The uncurling seems to separate the two rami a little laterally. Each ramus, at

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least in the two or three anterior pairs, can be moved to a certain extent, independently of the other ramus of the same cirrus; and the few terminal segments, either of both rami or of one ramus, are often a little moved and curled (and this is especially the case with the long anterior ramus of the first pair), without the lower segments or the pedicel being moved.

The flexor and extensor muscles, which, as I believe, move the upper segment of the pedicel (a and b, Pl. 29, fig. 1), are attached at their upper ends to its basal margin, and are thus enabled to draw it a little way down within the lower segment, and so move it. The short flexor muscle (c), which is attached at its lower end within the upper segment of the pedicel, and the longer extensor (d), also, attached within this same lower segment, serve, I believe, to move the lower, partially confluent segments of each ramus as a whole. In the case of these muscles, and of those last mentioned, I am surprised that the extensors (b) and (d) are not attached nearer to the exterior and dorsal surface. Other muscles (e, f) attached at their lower ends within the upper segment of the pedicel, run up each of the two rami to their tips, with some of the fasciæ terminating within each segment: of these muscles, the outer one (f, f) appears to be the extensor, and the inner one (e, e) the flexor. But besides these, there are other short flexor muscles (g, g) which run on the anterior face,* from segment to segment, serving to pull the front edge of one segment within the edge of the next lower segment. These muscles differ much in plainness in the several genera: they are very distinct in Coronula. In some specimens of this genus, a few of the articulations between the basal segments of the rami having been obliterated, the short muscles (g, g) running from articulation to articulation were absent, and their presence and nature in the upper segments thus rendered the plainer. The muscular system in the several pairs of cirri seems to be the same, with the exception of

* For a considerable time I thought that there were muscles going to the spines, especially to those which arise from the upper dorsal edge of each segment; but I have since ascertained that these are the cases within which new spines, with their lower ends doubled like the fingers of a glove hastily pulled off, are in process of formation.

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the first pair, in which the muscle answering, as I suppose, to (a), namely, the flexor of the upper segment of the pedicel, is much spread out at its lower end, and is there attached to the exterior surface of the lower segment.

The backward and forward movements of the segments, both in the rami and in the pedicels of the cirri, are apparently effected, as already noticed, by the outer or inner (as the movement may be) basal edge of one segment being drawn a little way down within the next succeeding lower segment. If, at the same time, both the inner and outer margins of all the segments were drawn one within the other, the whole limb would necessarily be shortened; and I distinctly saw a shortening action, with very slight movement in any other direction, in the first and second pairs of cirri; and I think it almost certain that this movement might be performed by the other cirri. If I correctly understand a statement of Milne Edwards,* this is an important fact, as he asserts that only the higher Crustaceans possess the power of shortening their limbs.

When a Cirripede is alive, the action of the cirri is really beautiful: from the position of the thoracic segments, the posterior cirri (three pairs in the Balaninæ and four pairs in the Chthamalinæ) form a sort of semicircle facing the mouth: the anterior cirri stand further apart, and are opposed in pairs to each other, with the first pair pointing beyond the mouth. Together the cirri form a hollow cone, not circular but elongated, with the mouth situated at the lower anterior end. The posterior cirri are protruded, by the movement of the whole thorax, curled up, close along the carinal end of the orifice; as they are protruded, they diverge, both by the movement of their pedicels, and, as I believe, by the separation of the thoracic segments. As the two rami of each separate cirrus are uncurled, they also diverge a little; as do the double rows of spines on the segments in each ramus, by their elasticity. By the movement of the thorax, the cirri are then swept towards the rostrum; and, lastly, they are brought perpendicularly down towards the mouth with a rapid movement, which would be beautifully adapted to catch any object floating or swimming in the water; hence

* 'Annales des Sciences Naturelles,' tom. xviii, 1852, p. 121.

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I have called the action of the cirri, captorial. When the shell of a Balanus is broken open, the second and third pairs of cirri are repeatedly clasped over the mouth with a convulsive movement, in a manner indicating, I think, that their chief function is to seize and carry to the mouth any object entangled by the sweeping movement of the three posterior pairs. The first pair is also well adapted to aid in this seizing action; but I suspect that the long anterior ramus likewise acts as an organ of touch, warning the animal of danger. The mouth being itself moveable as a whole,—the outer maxillæ being capable of a backward and forward sweeping action, and being furnished with orifices apparently olfactory,—the inner maxillæ having more diversified movements,—the toothed mandibles overhanging the œsophagus,—and the œsophagus itself possessing a powerful swallowing movement, are all admirably adapted to secure any prey, when once entangled by the cirri.

Mouth.

The mouth, in the sub-family Chthamalinæ, cannot be distinguished from that of the Lepadidæ, which has been pretty fully described in my former volume. In the Balaninæ, however, the labrum differs considerably in not being swollen; that is, in its outer and inner fold of membrane being close together, and in having a central notch: the palpi are also larger, and the lower teeth on the mandibles, are laterally (Pl. 26, fig. 5) double, as will be more particularly stated under these two sub-families. I have given a drawing (Pl. 26, fig. 1) of the mouth, seen from above, of Balanus perforatus, with the right-hand palpus (d') and outer maxilla (a') cut off, in order that the labrum (e), mandibles (c), and inner maxilla (b) might be better shown; the cut-off bases (x, x) of the first cirrus on each side are also shown. In fig. 2 we have the deep supra-œsophageal cavity in Bal. improvisus torn open and laid flat, with the inner surfaces of the labrum (e) and outer maxillæ (a) exhibited, the palpi, mandibles, and inner maxillæ having been removed. Figs. 3 and 4 will presently be referred to; they are parts of the mouth, with the mus-

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cles, &c. removed, of Coronula. The mouth differs extremely little in the different genera and species of the Balanidæ, much less than amongst the Lepadidæ. In the Balaninæ, the crest of the labrum is sometimes hairy, instead of having, as is usual, from two to six teeth on each side of the central notch: in Balanus improvisus (Pl. 26, fig. 2) and eburneus, and in Chelonobia, the crest on each side of the central notch (e') is furnished with a row of finely graduated teeth. A sub-triangular portion of the inner fold of membrane of the labrum, which overhangs the œsophagus, is always thickened and yellowish; it is also often punctured in patterns (Pl. 26, fig. 2, f), which, I believe, give attachment to little muscles that serve to open the upper end of the œsophagus. Opposite to this thickened, sub-triangular portion of membrane, the thin membrane forming the supra-œsophageal cavity (or the cavity surrounded by the gnathites) is strengthened by a pair of curved ribs (h, fig. 2) of thickened yellowish membrane, running down from the inner bases (a") of the bilobed outer maxillæ to the opening of the œsophagus (g): a broad branch from each of these ribs supports the sides of the orifice of the œsophagus; and this branch almost joins on to a slightly thickened rim or bar (f'), which branches off from the upper part of the sub-triangular (f) inner fold of the labrum. This structure, in Bal. improvisus, is represented in Pl. 26, fig. 2, as well as it could be, considering that the deep supra-œsophageal cavity has to be torn open, and then laid flat.

The Palpi (Pl. 26, fig. 6) differ little, except in size, in the different genera, being squarish, more or less elongated, or even approaching to club-shaped: in most of the Balaninæ they are larger even than the mandibles, of which they normally form a part. Their upper margins, especially towards their free extremities, are always thickly clothed with spines; and there is generally a single row, either short (r) or long, of spines of greater length, which arise from a little above, and stand almost in a parallel line to, the basal margin. On the internal surface, there is sometimes a row (t) of very short little spines, which overhang the crest of the labrum. The Mandibles (Pl. 26, fig. 5) have from

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three to five teeth; the lower point or angle is generally pectinated. In Coronula and its close allies, there are some small teeth intermediate between the four or five main teeth; and in these genera, though members of the sub-family Balaninæ, the lower teeth exhibit only rudiments of being laterally double.* The Maxillæ sometimes have a notch under the upper large pair of spines, and in Octomeris brunnea there is a double notch: in many species of Balanus, the inferior corner stands up like a step (Pl. 26, fig. 7, a): in many other genera and species, the whole edge is straight. In all, or almost all cases, the row of spines on the middle portion is double. The Outer Maxillæ are always bilobed on their inner faces, and are clothed with bristles. On all the gnathites, the bristles are often doubly serrated.

Muscles and functions of the Gnathites, and their confluence.—The outer maxillæ appear at first like a deeply-lobed lower lip, for they reach over almost to the labrum (Pl. 26, fig. 1), and thus partially cover the other organs; they are separately capable of a strong and rapid, to and fro movement, by which no doubt they sweep any prey, entangled by the cirri, towards the other gnathites. Each outer maxilla is furnished with a pair of muscles, apparently a flexor and extensor; there is also a little muscle between the two maxillæ, I presume for the purpose of bringing them together. The outer and inner maxillæ generally stand close together, and in several genera a little way apart, from the mandibles; but there is no trace of any labium or true lower lip, bounding the mandibles and orifice of the œsophagus. The outer and inner maxillæ and mandibles are not opposed in pairs to each other, but against the thickened inner fold of the labrum; almost in the same manner as the posterior pairs of cirri are not opposed one to the other, but to the mouth.

I have described pretty accurately the muscles of the

* M. Martin St. Ange describes, in his 'Mémoire sur l'Organisation des Cirripèdes,' pp. 15 and 32, "une petite langue" in the mouth of Lepas; but I may venture to assert that such does not exist; it is merely the point of union between the outer maxillæ. M. St. Ange, in his comparison of the mouth of Lepas with that of Phyllosoma, compares the mandible of the latter with the palpus of Lepas; the first maxilla of Phyllosoma with the mandible of Lepas; and so on with the other gnathites.

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mandibles in my former volume, and there given a drawing (Pl. 10, fig. 1) of them. There are four muscles: first, the depressor muscle, which is the largest, and is attached, at its upper end, to ligamentous apodemes under the free toothed portion of the jaw; and at its lower end, spreading considerably out, is attached to a concavity close above the basal margin of the labrum; to understand the action of these muscles, it should be borne in mind that the mandible almost faces the labrum. In some genera, as in Coronula,* the swelling near the basal margin of the labrum (Pl. 26, fig. 3, k), caused by the internal concavity for the above muscle, is conspicuous. The depressor muscle is opposed by a small elevator, attached to the mandible close by the depressor; thence it runs upwards, and is united at its upper end to the base of the palpus, at the point where the latter adheres to the labrum: I have ventured to call this muscle the elevator, from being apparently so well fitted for this purpose; but I feel some little doubt, from having observed an apparent slight movement in the palpi of living Balani; and this is the only muscle entering those organs. The free part of the mandible is articulated on a square, thickened piece of membrane, forming part of the side of the mouth (Pl. 26, figs. 3, 4, c 1; and Pl. 10, fig. 1, a, b, in my volume on the Lepadidæ); to this square piece of membrane, two short muscles are attached, one above the other, and which ought, in the Plate in my former volume, to have been represented crossing the depressor muscle at nearly right angles; at their further ends they are attached to about the middle of the labrum, where, at least in Coronula (Pl. 26, fig. 3, i), a slight concavity can be detected. The action of these two muscles must be to draw the whole mandible against the labrum; and the depressor muscle might, at the same time, draw the toothed edge downwards, and thus force any prey into the œsophagus.

The inner maxillæ are likewise furnished with four muscles, very nearly as figured in my former volume (Pl. 10, fig. 10); namely, two muscles, one inside and the other outside the curious apodeme, which in the Balanidæ (Pl. 26, fig. 7, b') is

* This is figured by Burmeister in his 'Beiträge zur Naturgeschichte der Rankenfüsser,' Tab. 2, fig. 6.

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as invariably present as in the Lepadidæ: these two muscles are attached at their lower ends to the outer membrane of the mouth, close to its basal articulation: the outer one of these two muscles would, I presume, act as an elevator, and the inner one as a depressor; the free part of the organ working on the top of the apodeme, like an axe, on a hinge, on the top of a pole. But there is also a larger depressor muscle, in an analogous position with that (i. e. the first-mentioned muscle) of the mandibles; and a fourth muscle, crossing the latter depressor at nearly right angles, and attached (as far as I could make out) on the side of the orifice of the œsophagus, close under the mandibles: the action of this latter muscle would be to draw the whole organ towards the labrum.

I must not conclude my description of the mouth, without drawing particular attention to its peculiar compounded nature. It is prominent, and is capable, as a whole, of movement; it is separated from the body by a fold or articulation, which can be traced all round. It is, as we have seen, composed of a broad labrum and three pairs of gnathites; which latter have only their terminal segments free; and these surround a conical hollow, at the bottom of which lies the opening of the œsophagus. The prominence of the whole mouth appears to result from the lateral fusion of the two basal segments of the three pairs of gnathites. I have examined the mouth of ordinary Crustaceans, and can see no trace of a structure like this. That there has been some union of the parts is indisputable; for the palpi, which in ordinary Crustaceans are quite free, are here firmly united to the upper and outer corners of the labrum; and indeed, at first appear to be more intimately connected with the labrum than with the mandibles. The palpus on its upper and exterior surface, is in direct continuity with the square thickened piece of membrane, on which the mandible is articulated, and likewise with that side of the upper or free portion of the mandible which faces the labrum. This face of the mandible, beneath the toothed edge, is hollowed out or arched (Pl. 26, fig. 5, p), owing to the above-mentioned continuity of its membrane with that of the palpus. On the lower surface, the palpus is

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firmly united to the lateral corners of the labrum; or indeed the corners of the labrum may be almost said to be formed by the soft, swollen bases of the palpi: the point of union, when viewed from the outside, is seen to form a knob on the shoulder of the labrum, beneath the level of its crest, and at this knob (Pl. 26, fig. 3, close to d') several thickened bands in the surrounding membrane unite. The free portion of the palpus stands out transversely behind (i. e. anteriorly to, in a homological sense) the labrum. I suspect that the palpus possibly may consist of two segments, of which the terminal one is free, and the lower one confluent with the labrum.

Before proceeding any further, I should observe that figs. 3 and 4, in Pl. 26, represent the membranes of the mouth of Coronula diadema, perfectly cleaned. In fig. 3, all the front part of the mouth has been removed, the mandible on one side, the labrum with the two palpi, and the œsophagus being alone left, and these are viewed from the inner side; the front part, however, of the supra-œsophageal cavity has been cut away. In fig. 4, the labrum, with the œsophagus, has been removed, whilst the two outer maxillæ, the right-hand inner maxilla and mandible (with the exterior and basal portions, d, d", of one palpus) are seen from the outside; but in order that these parts should all be shown, the whole of the right-hand side of the mouth has been spread out, for the teeth of the mandible should have stood in a vertical line between the two outer maxillæ. In the mandibles, the free upper part is separated, by a distinct articulation, from the square piece of thickened membrane (fig. 3, c 1) on which it is supported; and this latter is separated by a second articulation from a portion of thickened membrane (c 2), the basal edge of which forms the third and lowest articulation, separating the mouth from the body. This basal, thickened portion of membrane curls round and inwards, towards the outer maxillæ or front of the mouth, and its terminal points sometimes even penetrate a little way within the muscles, like apodemes: it is not distinctly separated by any line or suture from the membrane, which forms the whole broad labrum; so that I at first concluded that the labrum dipped under the mandibles, and thus afforded a support on which they were articulated; but this appears so opposed to all

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analogy, that it is more probable that the above basal thickened portion of membrane is truly the basal segment of the mandibles, completely confluent with the labrum; and it is, I think, not very improbable that even a large portion of what in appearance belongs to the labrum, namely, those concavities to which the muscles of the mandibles are attached, may, also, be part of the basal segment of the mandibles. Whether or no there really are two segments beneath the upper free portion of the mandibles, which have become laterally confluent with other parts, I must think that the square thickened piece of membrane (c 1) represents at least one segment. I may here observe, that Prof. Milne Edwards seems to consider the mandible of the higher Crustaceans as answering homologically to the haunch of the leg; but, according to M. Brullé,* there ought to be two basal segments (sous-maxillaire and maxillaire) bearing the proper mandible, and giving rise, on the outer side, to the palpus,—a structure which perfectly corresponds with my view of the mandible and palpus in Cirripedes.

Maxillæ: the point whence the long apodeme (b', Pl. 26, fig. 4 and fig. 7) arises, according to Audouin's views, must mark an articulation, and this would separate the upper free segment from the lower segments, which I believe to be laterally confluent with the organs on each side. The thickened membrane, of which the upper free part is formed, extends a little distance beyond the insertion of the apodeme; and this small portion beneath the point of insertion may possibly answer to the square, thickened piece of membrane, or second segment, supporting the mandibles. Beneath it, a rather wide expanse of thin, flexible membrane reaches down to the basal fold surrounding the mouth, and may thus form the third segment.

Outer Maxillæ: the upper free segment has a spinose lobe (a", Pl. 26, figs. 2 and 4), on its inner face, which may indicate a lower and second, almost free segment. Passing over this, we have, on the outside of the mouth, beneath the free, upper segments, an expanse of membrane, which, on the side, close to the inner maxillæ, is perforated (Pl. 26, fig. 4, n) by orifices which I believe are olfactory. In some species, as in Bal. eburneus and improvisus, there

* 'Annales des Scienc. Nat.,' 3d series, Zoolog., tom. ii, p. 271.

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is a longitudinal medial suture in this expanse of membrane, which I suppose indicates the lateral confluence of the middle segments of the two outer maxillæ. A short, transverse articulation or fold separates this middle segment fig. 4, a 1) of each maxilla from the third or basal segment; and this latter (a 2) is separated from the body by a very distinct fold, which (at least amongst the Lepadidæ) sends inwards a short, medial, tongue-formed apodeme. Here, then, we apparently have, as in the mandibles, two segments under the upper free segment of each outer maxilla, laterally confluent with the adjoining organs. But I must state that, in old specimens, and only in old specimens of Coronula diadema, I have found under the outer maxilla an additional transverse ridge and fold, which plainly shows how easily a mere thickening of the membrane might be mistaken for an articulation. I can, however, hardly persuade myself that the articulated membrane, under the free part of the mandibles, which has now been figured and described, has no homological signification; and the fusion of the palpus and labrum seems too plain to be mistaken. Hence I must conclude that the mouth, in the Cirripedia, does truly exhibit a compounded structure of a very peculiar nature.

Cirri.

There are always six pair; each biramous and multiarticulated, supported on a pedicel formed of two segments. A shield-like swelling at the exterior bases of these pedicels often appears like another segment; but such, I believe, is not its nature. The five posterior pairs answer to the five pairs of ambulatory legs in the higher Crustaceans; and as in the case of the latter, the three, or the four hindermost pairs almost invariably resemble each other. The first pair, which is homologous with the outer maxillipeds of ordinary Crustaceans, is separated by an interval from the second pair;—though this is not the case with the legs of the pupa, from which the cirri are metamorphosed. These anterior cirri are attached to the lateral edges of the mouth, namely to the thickened rim of membrane, forming the supposed basal

6                          

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segment of the mandibles. They are capable of more diversified movements than the other cirri: the anterior ramus is always elongated, with the terminal segments more or less tapering, and is directed beyond (or anteriorly to) the mouth: the shorter ramus closely resembles in structure the rami of the second pair. In the Chthamalinæ the second pair, and in the Balaninæ the second and third pairs (as will be more particularly described under these sub-families) differ in structure from the posterior pairs, from which they are separated by a slight interval. The number of segments on the posterior cirri is often great, amounting in Chelonobia even to fifty. Each segment normally is furnished on its inner face, which is usually somewhat protuberant, with from two to rarely eight or ten pairs of long spines or bristles, placed in a double row; the two spines in the lower pairs stand nearer to each other, and are shorter than the spines in the upper pairs. Between each pair of spines there is either a single, very thin bristle, or often a tuft of such. The pairs are directed somewhat upwards, and they diverge when the cirri are uncurled; their function is obviously to entangle the prey. On the dorsal or exterior surface of each segment, close to its upper margin, there is a tuft of spines, often composed of thicker and thinner spines; these, I believe, serve to prevent any creature intruding within the sack. On both sides of the upper margin of each segment, there is generally a row of short, blunt, excessively minute spines, which only deserve notice, inasmuch as it is by their increase in number and size, and by the spreading out of the dorsal tufts, and, lastly, by the increase of the little tuft intermediate between the pairs of spines situated in front, that the segments on the two or three anterior pairs of cirri become covered, like brushes, with bristles. The bristles or spines on the second and third cirri are often, especially in Tetraclita, doubly and coarsely pectinated. The bristles on the pedicels follow the same arrangement as on the rami; namely, being in regular pairs on the posterior cirri, and crowded thickly, like a brush, on the anterior cirri. The segments in the shorter ramus of the first cirrus, and in both rami of the second, and often of the third cirrus, are broader than

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the segments of the posterior cirri; they are, also, especially in the genus Balanus, frequently produced in their upper, ante-lateral corners, into remarkable prolongations (see Pl. 29, fig. 4, of the third cirrus of Bal. perforatus), clothed on their inner surfaces, and at their extremities, by numerous bristles. The number of the segments in each cirrus is in some degree variable, and increases with age; this is likewise the case, to a certain extent, with the number of the spines borne on each segment.

As compared with ordinary Crustaceans, I presume the two rami answer to the "tige" and "palpe" of Milne Edwards; and the pedicel (as I have called it) to the two basal segments of the leg.* The "fouet" or flabellum does not appear to be developed in any Cirripede; for though the filamentary appendages in certain genera of Lepadidæ, might at first be thought to be of this nature, yet their usual position beneath the basal articulation of the first pair of cirri, and the occasional presence of more than one, proves, I think, that such is not the case.

Though the structure of the cirri is very uniform, yet we meet with some peculiarities. In Chelonobia, the segments of the posterior cirri bear only two pairs of main spines; whereas in some varieties of Balanus balanoides, they carry as many as ten pair in a longitudinal row; but in this latter species, the number of these spines varies, in a singular manner, from six to ten pairs. In Tubicinella, the pairs of spines on the segments of the posterior cirri are arranged so closely one under the other, that they appear almost like a single transverse row. Considering the whole family, the third pair of cirri differs most in structure in the different genera. Thus, in Chthamalus antennatus, the anterior (or outer) ramus (Pl. 29, fig. 3) is thicker and much longer than the posterior (or inner) ramus; the number of the segments in one instance being, in the two rami, 53 and 18; in the longer ramus, the spines are arranged abnormally, tending to form a little circle round each segment; and

* According to this author's new nomenclature, the pedicel would consist of the coxopodite and basipodite; the tige would be the ischiopodite and following segments; and the palpe would be the exopodite; the epipodite or flabellum being absent. ('Annales des Sciences Naturelles,' tom. xviii, 1852.)

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the whole ramus may be said to be antenniformed, and I believe acts as an organ of touch: the relative number of the segments, I may add, in the two rami and the arrangement of their spines varies greatly in this species. In two other species of the same genus Chthamalus, we have occasionally the anterior ramus in some degree antenniformed, so that this whole structure is variable. In the allied Chamæsipho columna, it is the posterior or inner ramus which is antenniformed, but this peculiar development is more plainly marked in the case of the second pair of cirri than in that of the third pair. In Tetraclita porosa it is, also, the posterior ramus of the third pair which is antenniformed; in this third pair, and indeed in the other cirri, the relative numbers of the segments vary extremely. A similar structure in the third pair, but in a lesser and variable degree, may be observed in some of the other species of Tetraclita. In Balanus vestitus, also, we have, in the third pair, an analogous structure. It is scarcely possible to believe that the circumstance of the second pair of legs, which answer to the third pair of cirri, being antenniformed in certain decapod Crustaceans, is an accidental coincidence; it must be owing to some special affinity in the two groups.

In Chelonobia, the third pair of cirri is of unusual length compared with the second pair, but does not otherwise differ from the type of its sub-family: in Coronula and its allies, on the other hand, the third pair is very short and broad, as may be seen (Pl. 29, fig. 5) in Xenobalanus: in this latter genus, the front surfaces of the segments of the pedicels fig. 6) of the posterior cirri, are extremely protuberant, almost as in Scalpellum vulgare.

The last peculiarity in the cirri at all worth mentioning, is in the sub-genus Acasta, in which, differently from in all other known Cirripedes, the anterior ramus of the fourth pair does not absolutely resemble the rami of the fifth and sixth pairs; in most of the species, the spines on this anterior ramus are more crowded together, are larger, and are mingled with some short thick points; and the spines in the dorsal tufts are also longer than in the two posterior pairs of cirri; but in A. sulcata (Pl. 29, fig. 2), and in a lesser degree in A. cyathus and A. purpurata, the front margins of

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the lower segments of this anterior ramus, and of the upper segment of the pedicel, are developed into strong, downwardly-curved teeth: it is very remarkable that so beautiful a structure should be extremely variable, as it certainly is in Acasta sulcata.

Caudal appendages.—With extremely few exceptions, these are present in all the Lepadidæ and Verrucidæ; whereas amongst the Balanidæ they occur only in the two species of Pachylasma, and in one species of Catophragmus; these being the genera most closely allied to the Lepadidæ, and where, consequently, their presence might have been anticipated. These appendages are seated close together over the anus; they are multiarticulate, each segment being sub-cylindrical, with a few small bristles round its upper edge.

Alimentary Canal.

I have not much on this head to add to what I have said under the Lepadidæ. As in that family, the strong internal membrane of the œsophagus terminates in a remarkable, bell-shaped expansion (Pl. 26, fig. 3, g'), which, as observed by M. St. Ange, serves to keep the upper broad end of the stomach expanded. The œsophagus is well furnished with constrictor and radiating muscles for closing and opening it; and it is thus capable of a strong swallowing movement. The stomach runs down to the lower end of the prosoma, and then doubling back on itself extends to the anus. As the prosoma is much elongated in Tubicinella and Xenobalanus, so is the stomach of unusual length in these genera. In several species of Balanus, the upper edge of the stomach is surrounded by from six to eight cæca; these cæca I ascertained, in Balanus perforatus, are branched, and penetrate a considerable way into the body; and some of them at least expand a little at their extremities. Each cæcum, from the manner in which it retained fluid, must, I think, be furnished, at the point where it enters the stomach, with a sphincter muscle. In Tetraclita, Chthamalus, Tubicinella, Coronula, and Xenobalanus, there are no cæca; but in Xenobalanus and Coronula balænaris, there are longitudinal, approximate folds in the upper, broad end

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of the stomach, which would serve to expose the food to a greater extent of digesting surface.*

As in the case of the Lepadidæ, a transparent, structureless, epithelial tube, composed of chitine, containing more or less digested food, is found, in specimens preserved in spirits, occupying the whole length of the stomach, and where there are cæca, sending branched prolongations into them. It does not extend into the œsophagus or into the rectum. This epithelial tube or model of the stomach, filled with excrement, is expelled by the rectum, whole, that is in a single piece, as I observed in some living specimens of Balanus balanoides: in some specimens, however, of Chthamalus stellatus, the excrement was ejected, perhaps from the animal being confined, in fragments, and the sack thus became befouled. Beneath the epithelial layer, the stomach is lined by a delicate, pulpy and cellular mucus layer, which easily peels off in flakes: this is surrounded by a muscular layer with the fibres closely approximated and transverse; and this by a layer of stronger, longitudinal muscles, but more distant from each other. Lastly, outside this double muscular layer, there is a rather thick, somewhat laminated, pulpy layer, abounding with cells, often nucleated, and frequently containing much oily matter. This structure agrees closely with Dr. C. H. Jones's† account of the external covering of the stomach in Daphnia, and which he believes to be hepatic: as in Daphnia, there does not seem to be any ducts. I may here observe, that within the upper part of the prosoma, but not immediately connected with the stomach, I have often observed much white pulpy substance, permeated by lacunal passages, and exhibiting no structure except some excessively minute cells.

* The presence and absence of these cæca in genera so closely allied as Balanus and Tetraclita, shows, I think, that these cavities are not of high importance; and I must doubt whether Von Siebold's view ('Anatomie Comparée,' tom. i, p. 445), that these cæca form a passage to a true or isolated liver, such as exists in the higher Crustacea, can be admitted. Cæca are said by Von Siebold to occur in some of the Entomostraca, as Daphnia, Argulus, &c.

† 'Philosophical Transactions,' 1849, p. 116. Karsten ('Nov. Actorum Acad. Nat. Cur.,' 1845, tab. xx) has excellently figured the testes, as the hepatic glands; and has indicated the ovaria as salivary glands; it is singular that this anatomist overlooked the ducts which lead from his supposed hepatic glands, into the vesiculæ seminales, within which he observed spermatozoa.

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The rectum, lined by membrane continuous with that investing the thorax (and seen through it, in Pl. 26, fig. 8, c), extends inwards to about opposite the bases of the third or fourth pairs of cirri. It is longitudinally plaited; the ends of the folds forming a sort of valve where joined on to the stomach. It is coated by circular, transverse muscular fibres: judging from the movements, the anus itself is surrounded by a strong sphincter muscle. The anus opens on the dorsal surface of the thorax (fig. 8, b); but as in the genera, in which caudal appendages occur, it opens under them, the orifice, I believe, is homologically terminal, and owes its dorsal aspect to the aborted state of the whole abdomen, and to the great development of the probosciformed penis; for the anus may be said to be situated on the dorsal base of this organ.

Altogether we see that the alimentary canal is of a very simple structure. The food, judging from the contents of the stomach, seems generally to be composed of infusoria and minute animals: but in the case of Tetraclita, I have been surprised at the size and number of the included amphipod, isopod, and entomostracan Crustaceans, in one case, together with an annelid. I have, also, sometimes seen some confervoid matter within the stomach.

Circulatory System.—On this subject I can add nothing, except to express my conviction that there is no heart, or true vessels; the circulation being strictly lacunal. A passage has often been quoted from Poli, in which he states that he saw a pulsating organ, close above the anus; but I have seen this movement, which appeared to me to be a convulsive twitching of the sphincter muscle of this orifice. The largest lacunal channel extends down the middle of the rostral compartment of the shell: and this answers to the rostral channel down the peduncle in the Lepadidæ. Large nerves and the main pair of unbranched ovarian tubes (Pl. 25, fig. 1, leading into g) extend along this channel. At the basis (at least in Coronula) this channel joins on to a large circular one, running all round the sack, and sending off branches into the mass of ovarian tubes and cæca.

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Nervous System.

It has been shown in my former volume, that in Lepas and in some other genera of the Lepadidæ, there are six main ganglions; one supra-œsophageal, and five infra-œsophageal, or thoracic. In Pollicipes, however, there are only four thoracic ganglions, the last ganglion supplying the three posterior pairs of cirri with nerves, whereas in the other genera, the last ganglion supplies only the fifth and sixth pairs of cirri. In this genus, moreover, the lateral fusion of the ganglions has been so complete, that there is no evidence of their having been formed by the union of two. Amongst sessile cirripedes, we discover evidence of much higher concentration even than in Pollicipes. My chief examination has been confined to Coronula diadema, and to Balanus tintinnabulum: and in these genera we find (and the fact appears to me highly remarkable) as high a degree of concentration in the infra-œsophageal ganglion as in any decapod Crustacean, for instance, as in Maia, judging from the figure given by Milne Edwards; for all the nerves, with the exception of those connected with the supra-œsophageal ganglions, radiate from a single great ganglion.* The nervous system is, moreover, otherwise complicated.

To begin with Coronula diadema the great infra-œsophageal ganglion (Pl. 27, fig. 1, A) is seated nearly opposite to the anterior margin of the second pair of cirri, which are homologous with the first pair of legs in the decapod Crustaceans. This ganglion shows no trace of any longitudinal medial suture; its shape is hardly discoverable, for it is formed by the union of eleven principal pairs of nerves, besides

* It must, however, be observed that, according to Mr. Dana, there is in certain suctorial Entomostracans, as in Caligus, only one infra-œsophageal ganglion. Mr. Dana speaks of this as resulting from reduction. In Cirripedes, from the gradation which may be observed from Lepas through Pollicipes into Balanus, the ganglions are certainly not reduced but concentrated. In Van de Hoeven's figure of the nervous system in Limulus, there is seen to be no chain of thoracic ganglions; all the nerves rising from the circa-œsophageal collar; but this, on the other hand, seems hardly developed into a ganglion.

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several arising from its under surface; in outline, however, it may be said to be divided into a posterior and anterior half; the latter being somewhat heart-shaped, and the posterior half elongated. The nerves going to the five posterior pairs of cirri rise from the posterior margin of the ganglion, and run for some distance in a sheet, parallel and close together; the pair, however, going to the second pair of cirri soon branches off from the others. Each of these nerves enters at the inner and posterior margin of the cirrus to which it belongs, and, at least in the case of the first pair, divides into two branches as it enters. The nerves (Pl. 27, fig. 1, r 5, r 6) going to the fifth and sixth pairs of cirri are more closely united together than are the others, and appear, till they branch off, like a single large nerve. That which belongs to the sixth cirrus gives off, opposite to the fifth cirrus, a branch (s) nearly as large as itself, which enters the probosciformed penis. I may remark, that homologically this is the only abdominal nerve in any cirripede of the Order. From the under side of the nerves which run to the five posterior pairs of cirri, small branches are given off, extending dorsally into the thorax.

The anterior end of the great infra-œsophageal ganglion is formed by the union of a set of nerves, extending parallel in a bundle in a directly opposite direction to those running to the five posterior pairs of cirri. These nerves consist of an outer larger pair (r 1) entering the first pair of cirri; and within these, and rather dorsally to their roots, we have the circa-œsophageal chord (c, c), or collar nerve; between the roots of the latter, and on the ventral surface (or near side of the figure), there are three closely united, small pairs, running to the gnathites, and, as I believe, to the olfactory sacks. From the under (or dorsal) surface of the anterior end of the ganglion, two nerves, larger even than the circa-œsophageal chord, and which I shall call the splanchnic pair (d, d) arise; and the singular course of these nerves will presently be described; between this great pair, there is a single (b) medial nerve, which runs down and branches into that large diverging muscle, which is attached to the upper ventral surface of the stomach. Posteriorly to these three nerves, we have two pairs of much smaller nerves (not

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figured), running dorsally into the body, so that we have seven nerves rising from the under surface of the infra-œsophageal ganglion. I need only further add, that on each side of this ganglion, between the nerves going to the first and second pairs of cirri, there is a moderately sized nerve (k), which appeared to run into the muscles of the thorax: a nerve in a similar position is figured by Milne Edwards in Maia.

The circa-œsophageal chord (c, c) nearly equals in length the whole distance from the centre of the main ganglion to the posterior end of the thorax. This collar bows out on each side, where passing the œsophagus (œ), which is seated at its anterior end. From the collar a branch is given off on each side, which I traced as far as between the mandibles and maxillæ; from analogy with other Crustaceans, it perhaps runs to the mandibles. The collar has not a transverse commissure, such as described by Milne Edwards in the Podophthalmia, and as figured by Van de Hoeven in Limulus.

The supra-œsophageal ganglions (B) present a singular contrast with the infra-œsophageal ganglion in their little development, size, or degree of confluence. They lie directly under the basal edge of the labrum. They are laterally quite distinct, and consist merely of a slight enlargement of the circa-œsophageal chord. From the anterior edge of each ganglion, a broad nerve (f) extends for some distance in a straight line, and, on close examination, can be seen to be formed of two nerves closely united, of which the inner and smaller one, after a space, appears to cross over the larger nerve: both become at this point tortuous, and, giving off branches (m, m), form a plexus. The two nerves (f) then bend inwards, and almost touching each other, run down, together with the two ovarian simple ducts, along the rostral compartment of the shell. No doubt, if the smaller branches from these nerves could be traced, they would be seen to form a network over the whole sack; and would therefore enclose, as in a cage, the rest of the nervous system. These nerves correspond, I believe, to the two pair of antennular nerves of ordinary Crustaceans, and hence I will call them by this name.

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Just in front, at the outside corners of the two supra-œsophageal ganglions (B), a branch () arises, which I traced to the ends of the adductor scutorum muscle, and to those several muscles which serve to retract the interspace of membrane between the mouth and the adductor.

The pair of great splanchnic nerves above alluded to, which arise from the anterior and dorsal surface of the infra-œsophageal ganglion, are in Pl. 27, fig. 1, d, d, (and in fig. 2), laid flat; but in nature they first bow outwards, and then, penetrating deeper into the body, approach each other, and running nearly parallel, pass round the lower end of the œsophagus: their course consequently is nearly similar to that of the circa-œsophageal chord, with this difference, that the outwardly bowed portion is situated near the infra-œsophageal, instead of near the supra-œsophageal ganglion. The splanchnic nerve, a little beyond the supra-œsophageal ganglion, joins a plexus (); and into this plexus another large nerve (e) which I will call the supra-splanchnic nerve, sends branches; this nerve takes an almost semicircular bend over the ovarian glands. The supra-splanchnic nerves (e, e), though appearing to spring from the supra-œsophageal ganglions, do really arise, as may be seen by tracing the constituent fibres, from the circa-œsophageal chord. The plexus () lies close to the coats of the upper end of the stomach: several branches, proceeding from it, run further on, but I was able to trace only a few of them: one went (at least in the case of Balanus perforatus), to the adductor scutorum muscle: another branch spread out on the flanks of the prosoma: I strongly suspect that one branch goes to the acoustic sack: it appeared, also, as if some of the small branches entered the second plexus (m), where the inner antennular nerve and ophthalmic nerve cross over the outer antennular nerve.

I have called the nerves (dd, ee) splanchnic and supra-splanchnic, from their course and apparent function in supplying the viscera. In the descriptions of the nervous system of other Crustaceans I can find nothing analogous to my great splanchnic nerve (dd); the so-called supra-splanchnic nerves (ee), which arise from the circa-œsophageal chord, seem to be the analogues of the ordinary splanchnic

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nerves, though these latter are always described as uniting into a single medial branch. The plexus () is the cervical ganglion of M. Martin St. Ange,* who has likewise indicated the course of my splanchnic and supra-splanchnic nerves; but the plexus, when viewed as a transparent object, hardly appears to me to be ganglionic in its nature. In my former volume on the Lepadidæ, I quite misunderstood the course of these splanchnic nerves.

From the commissure between the two supra-œsophageal ganglions, a straight chord (Pl. 27, fig. 1, g) arises, which terminates in a small ganglion (C), barely exhibiting traces of being formed of two laterally confluent ganglions. This is the ophthalmic ganglion. The chord connecting it with the two supra-œsophageal ganglions is accompanied by a small nerve (h) which runs on to the muscles round the adductor scutorum muscle; the chord is encased by much fibrous tissue, and its dissection is thereby rendered difficult. From the ophthalmic ganglion, on each side, a nerve (i) goes forth and crosses the antennular nerve; these, if I could have traced them, would have been found to run, as may be safely inferred from what is known in Balanus tintinnabulum, to a pair (D, D) of eyes.

In Balanus tintinnabulum, the structure of the great infra-œsophageal ganglion (Pl. 27, fig. 2, A) is essentially the same as described under Coronula. The great pair of splanchnic nerves springing from its under side, are here actually twice as large as the circa-œsophageal chord. The plexus () formed by the splanchnic nerve (d), on each side, with the supra-splanchnic nerve (e), which arises close posteriorly to the supra-œsophageal ganglion, is here much less complicated, but is perfectly distinct; and there was no appearance of the cervical ganglion of M. Martin St. Ange. The chord (g) running from between the two supra-œsophageal ganglions to the ophthalmic ganglion, is nearly as large as the double antennular nerve (f) on each side of it. The ophthalmic chord (which is accompanied in its whole course by a small branch running to the adductor scutorum muscle) terminates in a small ophthalmic ganglion (C), which seems

* 'Mémoire sur l'Organisation des Cirripèdes,' p. 19.

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to be formed by the almost complete fusion of two ganglions. This ganglion is hardly larger than the chord which it terminates: it appeared to me to give rise to more than one pair of nerves, and a single nerve (to my surprise) joined the branch just mentioned, which goes to the adductor scutorum muscle.

From each supra-œsophageal ganglion, two closely united antennular nerves (f) extend, of which the inner one crosses over the main or exterior nerve, nearly opposite to the ophthalmic ganglion, and here forms (m) a plexus. The structure of this plexus I was not able, any more than in Coronula, to make out thoroughly, but I traced quite distinctly a long nerve (i) running from it into what must be considered as the eye. As in the case of Coronula, I traced a nerve on each side from the ophthalmic ganglion into the plexus, where I lost it; and as here in Balanus, I saw on each side of the ophthalmic ganglion a cut off nerve, of about the size of that which runs from the plexus on each side into the eye, I think we may safely conclude that the latter or optic nerve does really arise from the ganglion here called ophthalmic. I may add that the analogy of the nervous system in the Lepadidæ most strongly confirms the view of this latter being the ophthalmic ganglion.

The optic nerve (i), running from the plexus to the eye, is of considerable size; it runs nearly parallel to the main antennular nerve, diverging from it a little. It retains nearly the same diameter throughout; and gives off only one single, small, inner branch. It can be traced beyond the basal edges of the scuta, to just under the upper edge of the transparent opercular membrane, which unites the scuta to the sheath of the rostrum. The nerve itself, at a little distance from its further end, was, in a full-sized specimen, 5/1000ths of an inch in diameter; widening a little, it expands slightly, and abruptly terminates in a circular disc, about 8/1000ths of an inch in diameter, (see Pl. 27, fig. 5). The nerve just beneath this slight expansion, is coated all round by pellets of dark purple pigment-cells, but not actually united into a continuous layer. These pigment-cells are the more conspicuous from the surrounding parts being colourless. I could not make out distinctly any cornea; and I suppose the external

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transparent membrane, to which the above slight circular expansion is attached, acts as such. This description very closely agrees with that given of these organs in Bal. rugosus of Gould, (B. crenatus?) by Dr. Leidy,* who first discovered the eye in the adult cirripede, but he did not observe the ophthalmic ganglion. These eyes differ from those in some of the genera of the Lepadidæ, only in the greater length of the optic nerve, and by standing laterally further apart from each other.

I may here mention that I tried a few simple experiments on the senses of Balanus balanoides, B. crenatus, and Chthamalus stellatus. I found these three species very sensitive to shadows, that is, to an object like my hand passing even quickly, and at the distance of about a foot, between them and the source of the light.† They were indifferent to a gradual change from bright to obscure light; but instantly perceived and drew in their cirri, when my hand was passed between the basin in which they were kept and the window, even when this was tried rather late on a dusky evening; and likewise when my hand was passed between them and a single candle. I took, of course, the precaution of passing my hand in other directions, but this never produced any effect. These species are moderately sensible to any vibration in the vessel in which they were kept, but they were indifferent to noises made in the air, or in the water. I found it impossible to touch, under water, an individual shell ever so lightly with a needle, without all the immediately surrounding individuals, when several adhered together, perceiving it, and retracting their cirri: it made no difference whether the one touched had already withdrawn its cirri and was motionless: from this fact, and from seeing that a similar but slighter effect was produced by touching the rock on which the specimens adhered, I infer that the perception by the others of the one being touched, is communicated by vibration.

* 'Proceedings of the Acad. Nat. Sciences of Philadelphia,' vol. iv, 1848, p. 1. I may add that I have, also, observed the supra-œsophageal and ophthalmic ganglions in Bal. perforatus.

† I find that this fact was long ago observed by Von Siebold, 'Anatomie Comparée,' tom. i, p. 434.

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When an individual was touched under water, not by a needle, but by a pointed camel-hair brush, it generally withdrew its cirri, but the neighbouring specimens took no notice: when touched by a single hair of the brush, no notice was taken, unless the skin of the orifice leading into the sack was so touched. In these trials, it is of course necessary carefully to avoid intercepting the light. I could not make out that cirripedes perceived odours diffused in the water.

Acoustic Organs.—These are situated in the same position as in the Lepadidæ, namely, in a slight swelling on the sides of the thorax (Pl. 25, fig. 1, ) just beneath the basal articulation of the first pair of cirri. The orifice in Tubicinella and Xenobalanus is slightly produced, or is tubular; the free part in the former genus projecting 5/100ths of an inch. The structure of all the parts is essentially the same as in the Lepadidæ, but I think all are proportionally larger. The external membrane of the body is turned inwards at the orifice, as a short flattened tube, which widens considerably (being, in a middle-sized specimen of Coronula, 4/100ths of an inch in width) before it abruptly terminates. The meatus, as I have called the sack-like cavity which encloses the true acoustic sack or vesicle, is formed of pulpy membrane, and is apparently continuous with the corium of the whole body, but by dissection it can be separated entire. The acoustic vesicle is of various shapes, as we shall immediately see; but in all essential respects it is identical with the same part in the Lepadidæ; it is formed of the same peculiar, soft, elastic, brownish, transparent tissue, which seems to be composed of fine, transverse pillars, becoming towards the outside fibrous, and at their inner ends appearing when viewed vertically from above, like hyaline points. In Coronula diadema, I observed on the outside of the acoustic vesicle, some excessively minute bristles, only 1/3000ths of an inch in length, seated on little eminences. I examined carefully the contents of the vesicle in this species, in specimens well preserved in spirits, and there was nothing within but a very little, thin, pulpy fluid, and a few yellowish nucleated cells, here and there aggregated into small groups. In Coronula, the flattened acoustic vesicle is

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elongated, with a somewhat sinuous, but not very irregular margin (Pl. 27, fig. 4), and is without any ridges on the surface; its neck or orifice projects at right angles to the elongated portion, which stands obliquely to the tubular orifice of the meatus. In a moderately-sized specimen of Coronula diadema, the elongated portion of the acoustic vesicle was 6/100ths of an inch in length. In Tubicinella, the acoustic vesicle is heart-shaped, with the neck attached to its broader end; and the surface is covered by zig-zag ridges. In Balanus tintinnabulum (fig. 3), the acoustic vesicle is almost square at the lower end, with the neck placed at one of the upper corners; on the external surface, there is an oblique prominent ridge or fold, which sends off downwards another ridge; its length, in a large individual, was 5/100ths of an inch.

In all these cases, the acoustic vesicle is mainly attached by its neck, to the upper end of the sack-like meatus; but there is likewise a layer of soft, pulpy cellular matter, slightly connecting that side of the vesicle which is opposite to the neck, with the walls of the meatus or outer sack. The mouth or orifice of the vesicle is closed by a delicate lid or diaphragm, which can easily be separated; and this diaphragm is formed by the expansion of a large nerve, which here abruptly terminates. In a very large specimen of Coronula diadema I clearly made out the existence of this nerve, and traced its course for some distance from the point where the summit of the meatus and the neck of the vesicle are joined together; the nerve first runs posteriorly, and then turns inwards and doubles back or anteriorly; and I clearly followed it to the antero-lateral sides of the uppermost end of the stomach, where it seemed to enter a ganglion, so that I unfortunately cut it off, but found only a slight plexus, with the cut off nerve apparently running onwards with nearly the same diameter. The diameter is great, fully equalling, in its widest part, that of the circa-œsophageal chord; but it is very much flattened, and so has not nearly so much bulk as that nerve. Before it reached the stomach, it gave off one branch, which ran towards the mouth. The only nerves which, from their size, could, I think, be continuous with this from the acoustic sack, are

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the main branches proceeding from that plexus () formed by the interbranching of the splanchnic and supra-splanchnic nerves.*

Olfactory sacks.—I can add nothing to the account given of these organs under the Lepadidæ: I saw them in all the genera which I examined for this object. In Coronula diadema the orifices are large; they are seated in the usual position (Pl. 26, fig. 4, n), in the confluent segments, beneath the free part of the outer maxillæ, and somewhat exteriorly, or as near as possible to the inner maxillæ. In no sessile cirripede are the orifices produced or tubular, as is the case with several genera amongst the Lepadidæ. I failed, as heretofore, in tracing with certainty the nerve, which appears to enter the base of the sack, to its ganglion.

Reproductive System.

Male Organs.—All the Cirripedes of the family we are now describing, are bisexual or hermaphrodite; and no instance has been observed of the presence of males or complemental males. I have very little to add to the observations made by M. Martin St. Ange and R. Wagner,† and to those given in my former volume. The testes seem always to be confined to within the thorax, including the prosoma. With their ducts, they resemble club-moss or

* I have always feared that anatomists would reject my view of these organs being acoustic, owing to the absence of otolithes; but I observe that so high an authority as Von Siebold ('Anatomie Comparée,' tom, 1, p. 433) does not believe that otolithes occur in the acoustic organs even of the highest Crustacea. He considers an "ampoule volumineuse, a parois mince, remplie d'un liquide transparent," and a "membrane tympanique," though having a fissure in the centre, as sufficient. I may here remark, that the nerve proceeding from the acoustic vesicle in Cirripedes, and apparently running to the splanchnic nerve, may easily be placed in connexion with the antennular nerves, by the second plexus (m) in figs. 1 and 2, pl. 27. I should infer from Von Siebold's remarks on his ampoule volumineuse in the higher Crustacea, that my acoustic vesicle answered to the labyrinth in higher animals.

† The 'Report' on M. Martin St. Ange's memoir was laid before the Academy of Sciences, July 14, 1834, so that I suppose it was read previously to this date. R. Wagner's paper was published in 'Müller's Archiv,' 1834, p. 467. Burmeister's 'Beiträge zur Naturgeschichte der Rankenfüsser,' was published this same year, 1834; so that these three authors published almost contemporaneously.

7                     

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stag's horns, with the extremities a little enlarged: a figure* of a small portion from Balanus perforatus is given in Pl. 25, fig. 2. It is quite surprising how like in structure and appearance the branching ovarian tubes often are to the testes with their ducts; but the latter are of smaller diameter. Two main ducts generally unite just before entering the broad, often reflexed, end of the vesicula seminalis: in Coronula balænaris, however, I observed four ducts entering this receptacle. The two vesiculæ seminales, lying within the thorax and prosoma, are usually very long and tortuous: they are formed of a thin inner tunic, which is strengthened by thicker reticulated lines, and of an outer layer of transverse fibres, which are either elastic, or probably muscular, as they serve to expel the contents with force when the end is cut off. The inner tunic is prolonged up the probosciformed penis, at the base of which the two vesiculæ unite.† The contents of the vesiculæ are commonly pulpy and cellular; and from the cells the spermatozoa are developed; soon after their development, they are, as it appears, expelled.

I have seen the spermatozoa in Balanus crenatus, perforatus, and balanoides, and in Chthamalus stellatus. The cells, from which the spermatozoa are developed, and which are often found in vast numbers within the vesiculæ, are on an average about 1/5000th of an inch in diameter. The spermatozoa differ remarkably within the vesicula of the same individual, according to their state of development. I have observed in B. perforatus and in the Chthamalus, that the shortest, and therefore, I presume, the youngest (Pl. 29, fig. 7, a), had a globular head with no projection in front: as they increased in size, this head became less in diameter, and a short tapering filament, (a, b,) like the tail, projected out of it. This anterior filament does not lie in exactly the same line with the posterior filament, which is straight as an arrow. In Bal. crenatus, the anterior filament was 1/2000th of an inch in length, and the posterior filament 4/2000th, giving a

* A far better figure is given by Karsten ('Nov. Act. Acad. Cæs. Nat. Cur.' 1845, Pl. 20, figs. 2, 3, 4), but under the erroneous supposition that these organs were hepatic.

† In Conchoderma aurita, the ducts, as shown by Burmeister ('Beiträge,' &c. tab. ii, fig. 17), unite half way up the probosciformed penis.

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total length of 5/2000th: in the longest and best developed specimens of Chthamalus stellatus, the nodular enlargement was much elongated and spindle-shaped, and not above half the diameter it had in the earliest stage; the posterior filament (measured from the front of the enlargement, this consequently being included) was 5/2000th in length, and the front part only 1/4000th, giving a total length of 11/4000ths of an inch. These observations agree pretty well with Kölliker's;* but this author states, that perfectly developed spermatozoa are absolutely without any nodular enlargement: if this be the case, I have never chanced to see the spermatozoa in their perfect condition. Mr. Bate, also, figures some (Pl. 29, fig. 7, c) in this state, without any enlargement.

The probosciformed penis lies adpressed on the under side of the thorax, with its apex generally projecting between the first and second pairs of cirri. It presents the same ringed or articulated structure as in the Lepadidæ: it arises from an unarticulated projection or support, which also forms the posterior border to the anus. This support often terminates, as first observed by Poli, in a very sharp point; but this point cannot be of much functional importance, for though present in Balanus balanoides, it is absent in the closely allied B. crenatus; in Tubicinella there is only a rudiment of this point; I have not observed it in any member of the Chthamalinæ. The strong, transverse and longitudinal muscles with which the penis is furnished, are attached to this support. The apex or orifice of the penis is, I believe, invariably surrounded by some bristles. Its length varies much, according to its state of contraction or relaxation; and this again, I believe, is dependent on the condition of the male secreting organs. In a small specimen of Elminius modestus, the penis was actually thrice as long as the whole thorax, including the prosoma: in Pachylasma and in Octomeris angulosa, the penis is very short, being equal only to once and a half the length of the pedicel of the sixth

* 'Annales des Sciences Naturelles,' (2d series), tom. xix, p. 348. Kölliker refers to Wagner's paper on the same subject, in Wiegmann's 'Archiv,' 1835, part ii, pl. iii, fig. 9. He also refers to Von Siebold's observations. Mr. C. Spence Bate has figured, in the 'Annals and Magazine of Natural History' (vol. viii, 2d series, 1851), the spermatozoa of Balanus balanoides, perforatus, and of Verruca (Clitia) Strömia, and of these I have given copies, Pl. 29, fig. 7.

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cirrus: in Octomeris brunnea, the unarticulated support is much elongated, being as long as the pedicel of the sixth cirrus, in which respect this organ resembles that of Ibla quadrivalvis, and of no other Cirripede. From the attachment of the penis at the posterior end and on the under side of the anus—from the position of the caudal appendages (where such occur) over the anus—from the position of these same appendages in the pupa—and lastly, from the position of the papilla-like penis in the abnormal Proteolepas, I infer that, homologically, the penis is situated at the apex of the abdomen, on its ventral surface; and that, consequently, this organ cannot be considered as the abdomen itself in a modified condition.

Female Organs.—I have scarcely anything to add to the statements in my former volume. These organs consist of the true ovaria, or glandular bodies seated on each side, not far from the basal edge of the labrum; of the main or unbranched ovarian ducts; and of the (Pl. 25, fig. 1, g) ovarian branching tubes and cæca. I traced distinctly in Balanus, Tetraclita, and Coronula, the two main ovarian ducts, running from within the prosoma to the layer of inosculating, branching, ovarian cæca* which overlie the basis. In Coronula diadema one of these main ducts was 1/100th of an inch in diameter. Though I traced these ducts near to the grape-like, glandular masses,† which I cannot doubt are the true ovaria, I did not succeed in tracing them into actual connection. As in the Lepadidæ, these ovarian glands lie on the sides, near the basal margin of the labrum, and almost under, but rather to the outside of the antennular nerves. The branching and inosculating ovarian cæca form a layer, which corresponds with the mass filling up the peduncle in the Lepadidæ. In Tetraclita they do not cover the whole basis, but are confined to the circumference; they, however,

* These are well described in Lepas, by R. Wagner, in 'Müller's Archiv,' 1834, p. 467. Von Siebold, I observe, refers to Burmeister as the first author who discovered the ovarian cæca within the peduncle; I had thought that M. Martin St. Ange had a prior claim.

† These are obscurely figured by Karsten ('Nov. Act. Acad. Cæs. Nat. Cur., 1845, Pl. 20, fig. 1 d) as salivary glands; they were so considered by Cuvier and M. Martin St. Ange: I may observe that salivary glands have not been positively recognised in any Crustacean.

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likewise extend up between the two layers of corium round the walls of the shell, and chiefly in the interspaces between the depressor muscles of the opercular valves. In Chelonobia, they enter between the radiating septa in the thickness of the walls: in Coronula diadema, they extend from over the basal membrane into the six large square chambers (Pl. 16, fig. 7, v) separating the radii and alæ: in Tubicinella they are confined to the basis: in Xenobalanus, they form a layer over the basis and likewise round the upper part of the peduncle-like body, which answers to the shell of other sessile cirripedes.

As after the most careful and repeated examinations of various Lepadidæ, I was convinced that there were no oviducts, so I have come to a similar conclusion in regard to the Balanidæ; the ova being brought to the surface, by the formation of a new membrane round the sack underneath them, and by the subsequent exuviation of the old membrane. The ova are united together by a most delicate tunic investing each egg; the ovigerous lamellæ being thus formed, as in the Lepadidæ. In the cases of Chthamalus stellatus, Balanus balanoides, and Platylepas decorata, I saw a pair of very distinct but fragile lamellæ. In Xenobalanus, the two ovigerous lamellæ form two sub-cylindrical packets, pointed at their lower ends and often cohering. There are no ovigerous fræna, for the attachment of the lamellæ; the ova being sufficiently well retained, as it would appear, by the well-closed shell. I have elsewhere stated my full belief that it is the ovigerous fræna which have been metamorphosed into the branchiæ of the Balanidæ. Most sessile cirripedes breed when very young; and I have every reason to believe that they breed several times in the year. The ova are ovate, and vary in length from 14/2000th of an inch in Chthamalus, to 19/2000th in some species of Balanus, in which this greater length was owing to a more elongated shape,—up to 25/2000th in some other species of Balanus. The ova are wonderfully numerous, especially in the genus Coronula.

I may here mention the singular case of some elongated specimens of Balanus balanoides, from Tenby, in South Wales: some of these presented nothing abnormal; but in no less than seven specimens, the two, three, or four poste-

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rior pairs of cirri, either on one or both sides, were in an almost rudimentary condition, being of small size and having a shrunk and wasted appearance. In six out of these seven specimens, the probosciformed penis was quite short and abruptly truncated, as if from abortion. By cutting off the truncated apex, and cleaning the external tissue, I ascertained that it was imperforate, apparently in all the cases, and I am certain of this fact in several of the cases. In three of the specimens, I examined the vesiculæ seminales; in one, I found some spermatozoa, but cohering together in a peculiar manner; in the second, there were no spermatozoa; and in the third, the vesiculæ were shrunk, empty, and quite rudimentary in size. So that these three individuals certainly could not have impregnated their own eggs; nevertheless, within the shell of these very three, there were perfectly developed larvæ: I am led to conclude from this fact, that adjoining specimens in a perfect condition had, by means of their long probosciformed penis, effected the fecundation of their imperfect neighbours. I need only further add, that some out of the above six specimens, with more or less aborted cirri and imperforate male organs, were infested by a peculiar parasite, allied to Bopyrus,* and that these specimens did not contain ova.

Metamorphoses and Homologies, throughout the Order of Thoracica.

In my former volume, the metamorphoses were described under three principal stages or heads; but whether these three included all the main changes, I was then hardly able to conjecture. But now I have reason to believe that such is the case, for in the genus Cryptophialus, belonging to the Abdominalia, the whole course of the metamorphosis, from the egg to the pupa, takes place within the sack of the parent; and I found, when having, on the coast of South America, numerous specimens to examine, that the egg-like larvæ (Pl. 24, fig. 15-18) could be naturally grouped into

* I have given a short notice on this parasite, in my former volume on the Lepadidæ, in a foot-note to p. 55.

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two main stages, but with many transitional intermediate grades (answering to the successive moults in the first stage of ordinary larvæ), before they passed into the third or pupal stage. And the first two stages in these egg-like larvæ of Cryptophialus, clearly seem to correspond with the first two stages in ordinary larvæ; for in both the chief changes are, the shortening of the terminal projection—the increase in size and approximation on the ventral surface of the anterior horns or cases for the antennæ—and the compression of the whole body. In all members of the Thoracica, the metamorphosis seems to run a remarkably uniform course. The larva in the first stage undergoes several moults and slighter changes—how many is not known—before arriving at its second main stage, which has been observed only in one single instance; and judging from Cryptophialus, this second stage passes abruptly by one moult into the pupal stage; and this, certainly, passes abruptly into the Cirripedial or mature stage.

Larvæ, first stage.—The larvæ in this stage are known, amongst the Balanidæ, in Balanus, Pyrgoma, Coronula, Platylepas, and Chthamalus; and these genera include all the principal forms. Amongst the Verrucidæ they are known in its one genus, Verruca. Amongst the Lepadidæ, in Scalpellum, Ibla, Alcippe, Lepas, Conchoderma, &c.; and in all these genera the larvæ present no important difference—hardly any difference which could be viewed as generic, were these larvæ independent animals,— as may be inferred, chiefly, from Mr. C. S. Bate's descriptions.* The abstract given in my former volume was not accompanied by any illustrations, and I have consequently here given (Pl. 29, fig. 8), a view of the larva, in the first stage before moulting, of Scalpellum vulgare: the natatory legs are not drawn with accuracy, only the relative position of the several organs having been carefully attended to. I have also had copied from Mr. Bate's memoir, a figure of the larva (Pl. 29, (fig. 9) of Balanus balanoides, in its first stage, before moulting, with its ventral surface exhibited; and another figure (with a few trifling alterations made after examining

* 'Annals and Magazine of Natural History,' vol. viii (2d series), 1851, Plates 6, 7, and 8.

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specimens most kindly sent me by Mr. Bate) of the larva of Chthamalus stellatus (fig. 10), in its first stage, but after moulting once. It should be observed that Mr. Bate has given a drawing of the larva of this latter cirripede, in the first stage, before moulting; and it does not differ essentially from that just referred to (fig. 9), of B. balanoides, but is rather more fully developed. These drawings suffice to show the character of the larvæ in the first stage, both before and after the first moult, and even after the second moult, throughout the Order of Thoracica. The larvæ sometimes undergo their first moult within the sack of their parent, as I have been informed by Mr. Bate, and as I have observed in Coronula.

I will now make a few remarks on these larvæ in the first stage, before and after the first moult, supplemental to those in my former volume. Their shape is oval, and the whole dorsal surface is evidently covered by a carapace. It is remarkable that the body exhibits no distinct articulations; those given by Goodsir* being certainly erroneous. Commencing at the anterior extremity, the eye varies considerably in the state of its development; in Platylepas decorata it is nearly circular, and in most of the specimens very distinct; whereas in the allied Coronula balænaris, before the first moult, it is very imperfect, but afterwards square and of considerable size. In Balanus elongatus, in the immature larvæ dissected out of the egg, the cellular matter which was in process of conversion into the eye, formed a transverse band, obscurely divided into two portions, and this seems to indicate that the single eye is in fact formed by the confluence of two eyes. In Scalpellum vulgare, this heart-shaped eye lies between a V-shaped muscle, the nature of which I cannot understand, and which has not been represented in (Pl. 29, fig. 8, a). I need only further add, that in Chthamalus stellatus, after the first moult, the eye exhibits, in specimens sent me by Mr. Bate, some appearance of tending to become double.

Arising posteriorly to the eye, we see in Scalpellum vulgare, a pair of minute curved horns (), directed back-

* 'Edinburgh New Philosophical Journal,' July, 1843, Pl. 3, 4.

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wards; and within these horns I distinctly saw an articulated organ. These horns are difficult to be distinguished, and probably could not be made out previously to the first moult, in any larva of less size than that of Scalpellum vulgare. But after the first moult, Mr. Bate has seen, in two species of Balanus, in Verruca and in Chthamalus (fig. 10, b), a pair of articulated organs, in this same position, evidently now forming antennæ, and directed anteriorly, and free from any envelope. It is somewhat important, as we shall presently see, to bear in mind that these antennæ first appear within an envelope or horn; and that I detected that they included an articulated organ, before I had heard of Mr. Bate's observations. These antennæ, from their small size, from being seated internally with respect to the horns containing the other pair of antennæ, and from the position which the latter assume in the later stages of the larva, I believe to be the first or anterior pair. Their position in appearance posteriorly to the large lateral horns, containing the second pair of antennæ, is probably due to the anterior cephalic segments having been driven inwards, the truncated outline of the front of the head, and likewise, probably, the position of the mouth between the bases of the natatory legs being thus caused.

In this same larva of Scalpellum vulgare, within the great lateral horns just alluded to (fig. 8, c), filiform organs, supporting rows of spines, could be distinguished; and these appeared to me to be antennæ. These horns or cases resemble in structure the smaller pair just described; they arise from the ventral surface, and can hardly, therefore, be considered as prolongations of the carapace. After the first moult (fig, 10, c) they are seen to have increased much in length: in some cases they are of considerable length before the first moult, as in Lepas: in the Balanidæ they seem to be generally shorter than in the Lepadidæ; but in Balanus elongatus I found them one third of the entire length of the animal. Whilst within the egg, these horns are adpressed laterally to the body, and so point posteriorly; afterwards they project rectangularly from the sides, or, as in Scalpellum vulgare, are directed somewhat anteriorly. As in the larvæ of all ordinary Crustaceans, as yet known, the an-

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tennæ are amongst the earliest developed organs; and as the first pair of natatory legs (Pl. 29, figs. 8-10, e) in these Cirripedial larvæ, might so very naturally be thought to be antennæ (as has been remarked to me by Mr. Dana), both from their structure and from their position a little anteriorly to the mouth, I am well aware that to prove my view correct, namely, that these horns are the second pair of antennæ in process of formation, it is not sufficient merely to have seen organs resembling antennæ within them; nor is it sufficient to advance the strictly analogical fact of the first-mentioned pair of antennæ, which in Scalpellum indisputably appear in their earliest condition within an envelope or horn. Further evidence is required, and this is presented in Cryptophialus, in which the lateral horns of the egg-like larva, in its first stage (Pl. 24, fig. 16), can be actually followed step by step until, in the second stage (fig. 17), just before passing into the pupa, the horns are seen to have become larger and more nearly approximated to each other on the ventral surface; and whilst in this condition, I several times dissected out the prehensile antennæ of the future pupa with every character perfectly recognisable. Hence I cannot doubt that in the larvæ of Cirripedes the law of development is, that in their very earliest condition, the small first pair of antennæ are enclosed in cases; and that the large second pair remain thus enveloped until the pupal stage. This conclusion, we shall immediately see, is in harmony with the late development of the succeeding appendages or organs of the mouth, which certainly do not appear in the first larval stage, and are not known to appear even till after the final metamorphosis.*

The mouth is more or less probosciformed (Pl. 29, figs. 8-10, d), differing considerably in this respect in different species of the Lepadidæ; and this, probably, is due to the larva being born in a more or less mature condition. Its exact position likewise varies, for it arises either between the first or second pairs of natatory legs. It is known, from

* According to M. Joly, ('Annales des Sciences Naturelles,' 2d series, tom. xix, p. 59) in the larva of the macrourous Caridina, the natatory legs appear before the gnathites or parts of the mouth; so that in ordinary Crustaceans there is no invariable order of development from the anterior towards the posterior end of the body, as has sometimes been supposed.

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Mr. Bate's observations, to have the power of movement. It is directed posteriorly, the œsophagus extending anteriorly; both these directions being the same as in the mature cirripede. Certainly during these early stages there are no jaws or gnathites; but the margin, answering to the labrum, is furnished with some short, thick, sharp spines, and with hairs. In Scalpellum vulgare the orifice of the œsophagus seems to lie rather beneath the upper prominent spinose edge, which, as just remarked, probably answers to the labrum; but this is one of the species in which the probosciformed mouth, at least before the first moult, is not much developed.

We come, now, to the three pairs of natatory legs: the first (Pl. 29, figs. 8-10, e) has throughout the order only one ramus, whereas the two succeeding pairs (f, g) are biramous. I must here remark that the straight and strong, and the curved plumose spines, with which these limbs, after the first moult, become furnished, now appear to me as more probably prehensile, rather than masticatory as I imagined in my former volume. That these spines are important organs to the larvæ I do not doubt. With regard to the homologies of these three pairs of limbs, my first impression was that they were the mandibles and the two pairs of maxillæ in their earliest condition; but I consider this view as quite untenable, for several reasons; viz., the wide interval between their bases and the mouth itself,—the somewhat variable position of the mouth with respect to the legs,—and the position which the latter occupy in the second larval stage.* A far more tenable view is that these three pairs of legs are the three pairs of maxillipeds, in their earliest condition, in accordance with the view of M. Joly† on the nature of the three very similar pairs of natatory legs in the larva of Caridina, a macrourous Crustacean. But, in Cirripedes, the three pairs of natatory

* Mr. Dana, moreover, has remarked, ('Crustacea: United States Exploring Expedition,' p. 1386), "that he knows of no instance of a mandible becoming so completely a leg, as to lose wholly the mandibular function even of its basal portion."

† 'Annales des Sciences Naturelles,' 2d series, tom, xix, 1843, p. 34. M. Joly's observations were made on the Caridina. I owe to the great kindness of Mr. C. Spence Bate, an examination of some larvæ of the allied genus

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legs, in the larva in the first stage, are apparently the very same as the first three pairs, in the larva in the second stage, and in the pupa. And in the pupa the first three pairs, which certainly correspond with the first three pairs of cirri in the mature animal, seem to me, for reasons presently to be assigned, to be the second, third, and fourth thoracic limbs. Hence I am led to the conclusion that the first pair of legs in the larva in the first stage, are homologically the second thoracic (answering to the third pair of maxillipeds in the higher Crustaceans), and that the two succeeding pairs are the third and fourth thoracic limbs; to be succeeded, in the pupal stage, by the fifth, sixth, and seventh thoracic appendages.

Lastly, behind the natatory legs, on the ventral surface, (Pl. 29, figs. 8, 9, i), the body is much produced, and terminates in a horny fork, which after the first moult (fig. 10, i), becomes much elongated. Anteriorly to this fork, on the ventral surface, there is another fork (l), and again above this I could distinguish, in Chthamalus stellatus, after the first moult, another fork (m), or at least a pair of short thick spines. From the structure of the forked abdomen in the known larvæ of the Podophthalmia, I presume that this portion of the body is the abdomen of the young Cirripede, but it is not at all plainly articulated. After the first moult, the posterior end of the carapace (h), which is always pointed, becomes much elongated and serrated on both sides;* reminding one of the structure of the carapace of the so-called

Hippolyte varians, and I found, on dissection, the view of M. Joly, that the three pairs of natatory legs are the maxillipeds, so far strongly confirmed, that they followed closely, with equal intervals, the mandibles and two pairs of maxillæ. The first pair of natatory legs in Caradina, in its earliest condition within the egg, is uniramous, like the first pair in the larvæ of Cirripedes. There is one fact which seems rather strongly opposed to the view of these three pairs of legs in the larvæ of the macrourous Crustaceans being the maxillipeds, which is that Capt. Du Cane ('Annals of Nat. Hist., 1838, vol. ii, pl. 6, and 7) observed only three pairs of limbs in process of formation posteriorly to the first three pairs, whereas there should be found, in accordance with M. Joly's view, five pairs, i. e. all five pairs of ambulatory legs. This one fact countenances the view, which I hold on the nature of the legs in the larvæ of Cirripedes during their early stages, namely, that they are the second, third, and fourth thoracic limbs, to be succeeded by only three additional pairs.

* I suspect that the account given by Goodsir ('Edinburgh New Phil. Journal' 1843) of the posterior points of the carapace and abdomen in the larva of a Balanus, is not quite accurate.

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Zoea, or larva of certain Podophthalmia. Situated under this posterior prolongation of the carapace, there is a swelling (n, with long hairs on both sides), which apparently lies on the dorsal surface of the spinose and forked abdomen; here, when the larva is compressed, the cellular and oily contents of the body burst forth; and I suspect that this swelling is the anus, for it is known from the researches of Rathke,* that the anus in the higher Crustaceans opens during the earliest periods dorsally.

Larva, second stage.—I have given, from Burmeister,† a lateral view (Pl. 30, fig. 1) of the one single specimen, ever observed of a larva in this stage, belonging, as is supposed, to the genus Lepas. The carapace has now greatly altered its character. The two fleshy projections, as so called by Burmeister, by which the larva adhered to the sea-weed, were supposed by this author to include the great prehensile antennæ of the pupa; from my observations, already alluded to, on the two projections (Pl. 24, fig. 17) in the closely analogous egg-like larva, in the second stage, of Cryptophialus, by which it also adheres, I have not the least doubt that this is the case. The small, internal, and anterior pairs of antennæ are, as it would appear, now aborted. The eye, according to Burmeister, has commenced becoming double; but the two approximate eyes are not as yet compound. The mouth is probosciformed (m), and does not differ much from its condition in the first stage; no gnathites were observed by Burmeister, and they could not be expected to be present, for they are not found even in the pupa. The mouth, which in the larva in the first stage differs in different genera, in being more or less advanced forward, here stands some way anteriorly to the natatory legs, as in the pupal condition. The first pair of legs is uniramous, and the two other pairs biramous; this fact, together with the number of the legs in this second stage being still three, and their structure being not very different, leaves little doubt on my mind that we here have the same three pairs as during the first stage. The abdomen has become much shortened, but still space is left for the development, in the pupa, of the three pos-

* 'Annales des Scienc. Nat.,' tom. xx, p. 451.

† 'Beiträge zur Naturgeschichte der Rankenfüsser', tab. 1, figs. 3, 4.

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terior pairs of legs. I may here remark that in the pupa the anterior natatory legs have become, like the others, biramous; but yet, as it were for the purpose of showing their metamorphosis from the uniramous legs of the earlier stages, they have their bristles arranged rather differently from those on the succeeding five pairs of legs.

Larva in the third or pupal stage.—I have given a lateral view of the pupa of Lepas australis (Pl. 30, fig. 2), illustrative of the description in my former volume: the specimen is drawn as if transparent, and it was to a certain extent thus rendered by boiling in caustic potash. A sketch of the position of the young Cirripede within the pupa, was made by the camera. At first the drawing will perhaps hardly be comprehended: the darker shaded portion to the left of the letter (b) shows the extent of the sack, with the included thorax and natatory legs of the pupa: to the right of the same letter, if we do not consider the young included Cirripede, the only organs distinguishable in the mass of cellular and oily matter, are the alimentary canal, the cement-glands (t), i. e. the incipient ovaria, and the cement-ducts () which enter the antennæ. A view is also given (fig. 4) of the ventral surface of the pupa; and a transverse section (fig. 7) of the carapace, taken close to the eye-apodemes. On comparison with the larva in the second stage, the changes in external appearance and structure are not very great; the prehensile antennæ are freed from their cases; the two eyes stand further apart; the three posterior pairs of legs have been developed, and a small abdomen has become distinctly separated from the thorax. Before proceeding to make a few additional remarks and corrections to my former description of the pupa, it will be advisable, on account of the importance of the subject, to discuss the homologies of the limbs.

From the presence of eyes and of two pairs of antennæ in the larva, during its earlier stages, the front of the head consists, in accordance with all analogy, of three segments; the mouth, likewise, from being formed of three gnathites (which can be detected by dissection in the pupal state), consists, also in accordance with all analogy, of three segments, making altogether six segments—on the

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nature of which I apprehend no objection will be raised. In two out of the three orders into which Cirripedes may be divided, the mouth is succeeded, in the adult animal, by eleven most distinct segments; of which the first (i. e. the seventh cephalic) differs from the succeeding seven thoracic segments; and these seven again differ from the three abdominal and terminal segments. Hence it must be admitted that, as far as the cephalo-thorax of the archetype Cirripede is concerned, it consists, like that of the archetype Crustacean, of fourteen segments, of which eight succeed the first-named six that form the mouth and front of the head; and that, with the three abdominal segments, there are altogether seventeen segments. In the order Thoracica, however, which includes all common Cirripedes, both in the pupa and in the mature animal, only six thoracic segments with their appendages, succeed the mouth, two having been lost; and the question arises which are these two, whether the seventh and eighth, or the thirteenth and fourteenth (i. e. the two terminal thoracic) segments; for there is no reason to suspect any other segments of having disappeared. In my former volume, I inferred, without sufficiently entering into my reasons, that it was the seventh and eighth, i. e. the last cephalic and first thoracic segments, which had disappeared; but I now find that Mr. Dana* believes that, in ordinary Crustaceans, the abortion of the segments with their appendages almost always takes place at the posterior end of the cephalo-thorax. Nevertheless, after due deliberation and fresh examination of the pupa, I must retain my former opinion, that it is the last cephalic and first thoracic segments which have either coalesced with the others, or wholly disappeared. In the pupa, the mouth, although functionless, has its place most plainly marked by being slightly prominent, and by the presence of a sort of labrum and of a shrivelled œsophagus, round which latter the gnathites and the new œsophagus of the future young cirripede are in process of formation. Now between the mouth of the pupa and the first pair of natatory legs, there is a space of membrane, equalling, when stretched out, the three succeeding thoracic segments in length and breadth: this interspace, I conceive,

* 'Crustacea: United States Exploring Expedition,' p. 22.

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must have some homological signification; here then we have at least an appearance of the abortion of appendages; whereas, at the posterior end of the cephalo-thorax, no such appearance is presented. Moreover this interspace of membrane is divided nearly in the middle by a most conspicuous fold, which, on the view here adopted, would mark the separation of the seventh (cephalic) from the eighth (thoracic) segment; and the interspace and fold are thus simply explained. Lastly, I have shown, in the Introduction (p. 18), that the first and five succeeding pairs of cirri of the mature Cirripede present certain small, but significant, resemblances in structure and in the origin of their nerves, with the outer pair of maxillipeds and with the five pairs of ambulatory legs in the Podophthalmia; which resemblances are all futile, if the cirri belong to the 7th, 8th, 9th, 10th, 11th, and 12th segments of the cephalo-thorax, or those immediately succeeding the mouth; but are full of meaning, if the six pairs of cirri belong, as I believe, to the 9th, 10th, 11th, 12th, 13th, and 14th segments, or the six posterior segments of the cephalo-thorax.

Before commencing on details, I may premise that I have examined the pupa of Lepas australis, pectinata, fascicularis, and anatifera, of Conchoderma virgata, partially of Dichelaspis Warwickii, of Ibla quadrivalvis, and of Alcippe lampas; and in the Balanidæ, of Balanus balanoides and Hameri. In the pupæ of all these genera there is a most close general agreement in structure, excepting in minute details: I was surprised to find exactly the same slight differences in the spines on the first pair of natatory legs, as compared with the succeeding pairs, in Balanus Hameri, as in Lepas. The abdomen and caudal appendages of the pupa in the abnormal Alcippe, as we shall presently see, offer the only marked exception to this uniformity of character throughout the Thoracica. The outline of the carapace or shell is usually not so blunt at the anterior end, as in the pupa of Lepas australis (Pl. 30, fig. 2); more commonly the shape is that of the pupa of Alcippe (Pl. 23, fig. 16). In Lepas pectinata the two posterior points of the carapace are produced into two short spines. The surface of the carapace in L. australis is lined, as represented in fig. 4:

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the colour of this species when alive was blue:* in L. fascicularis the surface is punctured: in L. pectinata it is marked with curious points of various shapes, often star-shaped, in parts reticulated, and confluent along the dorsal margin, and in parts lined: in B. balanoides it is very obscurely punctured, and in B. Hameri the punctures pass into lines. The whole of what is externally visible consists of the carapace, for this is produced not only backwards, so as to enclose the thorax and abdomen with their appendages, but also forwards, so as to overhang the whole front of the animal; and the prehensile antennæ, in Lepas, Ibla, Balanus, and probably in all the genera, can be retracted within its lower edge. The protection afforded by the carapace to the antennæ is aided by two crests (Pl. 30, fig. 7, c) parallel to this lower edge. The whole sternal surface is very narrow (fig. 4), and is likewise protected by the carapace; that is, when the two sides are drawn together by the adductor muscle. The shell, however, when thus drawn together, gapes a little at the two ends, at least in the case of Lepas australis. The adductor muscle, if introduced in fig. 4, would have crossed close anteriorly to the basal margin of the mouth; and in fig. 2, its end on the near side would have been attached under the dark cæca, which enter the upper end of the stomach. The adductor is shaped almost like an hour-glass, and so differs from this muscle in the mature Lepas, in which it is of the same thickness throughout. I may here add that the pupa of Lepas australis could swim very rapidly, and often on one side in a circle; it could walk by the aid of its antennæ, but often fell over; being thus locomotive, and, as we shall immediately see, well provided with senses, it cannot be considered as very lowly organised.

Acoustic Organs.—Commencing at the anterior end, two small elongated orifices, 10/6000th of an inch in diameter, (e, fig. 4, Pl. 30), may be seen; these lead, as described in my former volume, into a sack, with a bag suspended in it, which is provided with a large nerve, and which I believe

* I took this species alive in the Southern Atlantic Ocean; and, mistaking it for an independent Crustacean, was much perplexed where to class it. I had overlooked these specimens when publishing my former volume.

8                           

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to be the acoustic vesicle. These orifices occur in the carapace, either in the same position, or a little more posteriorly, in the pupæ of all Cirripedes. In Balanus balanoides they are minute, being only 2/6000th in diameter, but are surrounded with a border: in Conchoderma virgata they are also surrounded by a border: in Lepas pectinata, the orifices are 3/6000th of an inch in diameter, and are very singular from being seated on rounded prominences, causing the carapace to have two short, blunt horns in front. In Lepas australis, and I believe in the other species, the corium round the acoustic orifices is darkly coloured; and these coloured marks can be distinguished for some little time on the peduncle of the young Cirripede, after the metamorphosis, and after the entire organ, together with the whole pupal carapace and eyes, has been moulted. Knowing the connection in the higher Crustacea, of the acoustic organs and the antennæ, and seeing the very backward position (figs. 2 and 4) of the one great pair of antennæ, I have always imagined that these orifices probably marked the normal position of the anterior pair of antennæ, which, since the earlier larval stages, have disappeared. And I now find* that Schödler affirms, that in most, if not in all Daphnidæ, there is a black spot in front of the eye, which is connected with an opening in the basal portion of the anterior antennæ, and he concludes that it is an organ of hearing.

Antennæ.—These, from their present position, and from standing, in their earlier stages whilst within their envelopes or horns, exteriorly to the small medial pair (since aborted), I believe to be the second pair; and this is Mr. Dana's opinion. In my former description of these very singular and important organs (Pl. 30, figs. 4 and 8), I have fallen into some considerable mistakes: the two plates or segments fig. 4, N), of which the posterior margins are inflected as apodemes (n), carrying the eyes, are certainly, as may be clearly seen in the pupa of Alcippe, Pl. 23, fig. 16, and as affirmed by Burmeister,† the basal

* Quoted by Dana, 'Crustacea of United States Exploring Expedition,' p. 1264.

† 'Beiträge zur Naturgeschichte der Rankenfüsser,' p. 19. In tab. 1 of this work there are good drawings of the general structure of the pupa of a species

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segments of the antennæ. The second or main segment (formerly called by me the basal segment) has in some species an upper portion of the membrane of which it is composed, next to the body, excessively thin, and separated from the rest of the membrane composing the segment, by an oblique line (fig. 8, o), which I mistook for its articulation with the body.* We then come to the disc or third segment; and lastly to the fourth, or ultimate segment. This ultimate segment, generally, has its external corner projecting up, as a step; and this sometimes, as in Dichelaspis Warwickii, gives the appearance of its consisting of two segments; but a careful examination of this part in Ibla, in which the step-like structure is carried to an extreme, makes me believe that there is only one segment.† The prehensile antennæ, therefore, like the natatory legs, are formed of four consecutive segments, of which the basal segments give rise to the singular apodemes, presently to be noticed (fig. 7), that carry the great compound eyes. This basal segment, in all Cirripedes, is moulted with the eyes, the three other segments invariably remaining cemented to the surface of attachment.

In the Southern Atlantic I took some specimens of the pupa of Lepas australis, not yet attached, and therefore with the muscles of the antennæ, not having suffered any of that absorption, which they undergo, as soon as the pupa is permanently cemented to some floating object. In my former volume I noticed a pair of strong muscles, attached to the tips of the middle forks (Pl. 30, fig. 7) of the apodemes, and I now find two pairs attached to the bases of the two outer forks, and directed dorso-anteriorly; and two other

of Lepas, probably L. australis. I believe this author was the first who made out the structure of the abdomen of the pupa.

* In the table of measurements of the antennæ of the several genera and species of the Lepadidæ (p. 286) of my former volume, the articulation, called by me basal, I now know to be really the articulation between the basal and second segment. In the fourth column, headed "Length from end of the disc to the inner margin of the basal articulation," the term inner margin really applies to the oblique curved line separating the thin and scarcely visible membrane from the thicker membrane of that segment. These corrections do not in the least affect the object for which the table was given.

† In a sketch, sent me by Mr. Dana, of this organ in the pupa of a Lepas from the Antarctic Ocean, I observe that he divides my ultimate segment into two segments.

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pairs, also attached to their bases, but directed dorso-posteriorly, so that altogether there are five pairs of muscles attached to the apodemes; their chief function, I should think, was to draw the antennæ posteriorly and upwards within the carapace; but as the apodemes cannot be moved without the great compound eyes being likewise moved, the muscles probably serve a double purpose. When the pupæ were alive, I noticed that their eyes were constantly kept in a state of vibratory movement. Flexor and extensor muscles are attached at one end to the posterior margin of the basal segment, and at the other end to the second or main segment; other powerful muscles attached to this latter segment, are prolonged by ligaments into the disc. In Cryptophialus I observed that the disc-segment had a movement almost like that of the wrist. Whether any muscles enter the small terminal segment, I know not.

The drawing in Pl. 30, fig. 8, of part of the second segment, of the third or disc segment, and of the fourth or ultimate segment, in Lepas australis, is, I think, very accurate. The second segment articulates on the upper or dorsal surface of the disc, and has the articulation on one side constricted and formed of thin and flexible membrane; the little terminal segment, which is turned outwards at right angles, also, articulates on the disc. That the disc forms a true segment is shown clearly in Cryptophialus (Pl. 24, fig. 18), where the articulation with the second segment is not in such close contact. The disc is either circular, as in Lepas, or hoof-shaped, as in Ibla: in B. balanoides the disc is rather hollowed out on the inner side. It has the power of adhering even to so smooth a substance as glass, placed vertically. It is surrounded by a rim of transparent membrane. On the hinder margin some spines arise from the central and more opaque part: in Lepas australis, there are no less than seven of these spines (fig. 8): in Conchoderma virgata there are only four, in Scalpellum and Ibla only one. When the disc is placed on the surface of attachment, these spines lie parallel to it. The middle part of the disc is, almost always, nearly opaque; and in tracing the cement-ducts from within the body of the pupa, or of the young Cirripede, I in many cases traced them as far as this

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point, but here lost them. From this same obscure central part of the disc, in most, if not in all species of the Lepadidæ, spokes radiate, which sometimes are branched, and are not regular, not always even resembling each other on the opposite sides of the same individual. Round the proper membranous border of the disc, a second one may be observed (fig. 8, p), which differs in shape and extent in different specimens: under favorable circumstances, and very high powers, it may be seen to have a reticulated structure, and to be of a very pale brown colour; towards the exterior margin, the reticulations become finer, and are blended together and lost; on the inner margin, the substance forming this membrane may be seen to come out of the spokes. This substance is the cement, which has the power of adhering to whatever substance it grows against; and thus the disc of each antenna becomes cemented down, and soon both the antennæ are surrounded by a common border of cement, which gradually increases, after the metamorphosis, in extent. Occasionally the cement forms little projections, like short spines, on the edges opposite to the orifices of the spokes.

The small terminal segment usually bears on its truncated extremity six spines, some of which are occasionally hooked; in Scalpellum, two spines, rather longer than the others, are borne on a step some way down on the inner side of this segment; but in Lepas, two spines (fig. 8), very much longer than the others, arise from the outer corner of the extremity. These two are very different from the other four borne by this segment, or indeed any other spines on the body; for they are quite flexible, and are furnished with a double row of very long, straight, excessively fine hairs, which seem to be articulated on them—the whole presenting a very beautiful appearance. These spines are of considerable length, and in Conchoderma virgata they even equal in length the whole antenna. I can hardly doubt that these beautiful, plumose, flexible spines, into the thick bases of which the coloured corium could sometimes be seen to enter, serve as feelers. Owing to the facts immediately to be mentioned, I erroneously stated, in my former volume, that there were three long spines.

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In three species of Lepas, in Dichelaspis Warwickii, and in Scalpellum Peronii, after having torn the lately-cemented antennæ from the surface of attachment, I observed proceeding from the end of the terminal segment, from between the above two groups of spines, what appeared to be a long narrow ribbon with its end torn off; and which, in the case of Lepas australis, I fancied was one of the plumose, long, flexible spines ripped open. But now that I have examined some of the pupæ of this species before their attachment, I find (as represented in Pl. 30, fig. 8, ) a flattened tube, ending in a blunt point, and having a peculiar ringed structure. I have noticed similar appendages to the antennæ of specimens just attached of Lepas anatifera. In the Dichelaspis and the Scalpellum, the tube was very long, and seemed, from its torn appearance, to have been firmly attached to the supporting surface. In both these cases, the tube came out from within another slightly larger tube, which had been broken off close to the extremity of the terminal segment of the antenna. In the case of the Lepas anatifera, the tube expanded a little after leaving the antenna. In the Dichelaspis, it had exactly the same diameter as the cement-duct, which could be clearly distinguished within the two lower segments. From these several facts, and from the peculiar appearance of the tube itself, I believe it to be a tube of cement-tissue which thus, sometimes even before the pupa is attached, independently grows outwards. That the cement-tissue can grow outwards and assume definite forms, we know from the singular case of Lepas fascicularis, in which the cement proceeding from several apertures, forms a vesicular float round the peduncle of not only a single individual, but often of a group of specimens: we shall presently find a somewhat analogous fact in the case of Coronula. It is possible that this tube, proceeding from the extremity of the antenna, may be the channel through which cement continues to be poured forth during the continued growth of the above Cirripedes; and the manner in which this is effected, considering how firmly the end of the peduncle is cemented down, has always appeared to me a difficulty. In those pupæ of Lepas australis, which I caught swimming about unattached, it is

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surprising that the disc should have been edged with cement, and that a tube, similarly formed, should have grown out of the ultimate segment: it shows, I presume, that the cement-tissue will grow out, whether or no the pupa has succeeded in finding a proper object for attachment. Lastly, I have felt some surprise, in two or three instances in observing some dark purple pigment-cells, like those in the corium, within the terminal tube of cement; and likewise within the spokes of cement in the disc: this is the only fact which causes me the least doubt, whether I have rightly determined the nature of the terminal tube, as wholly formed of cement tissue; or whether it may not be covered by an outer integument, itself lined by true corium, coloured purple.

Finally, I may add, that, excepting in small details, the prehensile antennæ present no difference throughout the Order: I have minutely examined them in several genera of the Lepadidæ; and in the Balanidæ, I have seen them in Coronula, and in several species of Balanus. In B. balanoides I have examined them carefully; they are smaller and thicker than in Lepas, with the second or main segment bowed outwards, carrying its usual single spine; with the disc excised on its inner margin and apparently without the spoke-like vessels for the cement; and with the ultimate segment proportionably longer, and carrying, I believe, six spines, of which two appeared to be longer and more flexible than the other four shorter and somewhat hooked spines. In Coronula balænaris, also, the terminal segment is, proportionably to the others, of large size. Not only throughout the order, but throughout the whole Class, the antennæ are singularly uniform in structure, as will be seen, when the last two orders are described.

Eyes.—These present no difference, except in size, throughout the class; and have been sufficiently described in my former volume. The true basal segments of the antennæ (incorrectly designated formerly as sternal plates or segments) are separated from each other by a deep fold; and are separated from the edges of the carapace on each side by a crest and slight fold (Pl. 30, fig. 7, c; and 4); these folds and crests die out posteriorly, and disappear. The hinder, rounded margins of the basal segments are

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inflected inwards, and their corners are produced far up into the body, thus forming the curious UU-like apodemes. These apodemes exist throughout the whole class; and the outer arms always carry the great compound eyes. I noticed, in Lepas pectinata, that the two middle arms are proportionably longer than in L. australis. Owing to the presence of these apodemes, and to certain coloured marks on the adjoining corium, the eyes, though inclosed fairly within the carapace, yet deceptively appear pedunculated, so that even J. Vaughan Thompson was thus deceived. I have already described the several muscles attached to these apodemes, and the constant vibratory movement of the eyes. Whilst the pupa remains a freely swimming animal, the eyes are included, not only within the shell or carapace, but (as would naturally happen) within the corium or true skin lining the carapace; but after the pupa has become attached, preparatory to its final metamorphosis (in the state represented at Pl. 30, fig. 2), not only are the muscles, as before remarked, which are attached to the apodemes, absorbed, but so is the corium investing the apodemes and the immediately adjoining parts of the carapace. Hence it comes that the new corium of the young Cirripede within, is formed in a deep transverse fold across the whole lower half of the animal, and the apodemes with the eyes are thus, as it were, rejected from within the corium, though still remaining within the carapace. Consequently in this final stage, the eyes and apodemes are very conspicuous from the outside, being seen only through the transparent carapace. I presume that the eyes at this period have become functionless, with the optic nerve divided and absorbed. The eyes, apodemes, and carapace soon afterwards are all moulted together.

The eyes of Cirripedes certainly undergo a remarkable series of changes: in the larvæ in the first stage, there is a single eye, perhaps formed by the confluence of two eyes, occupying the normal position in the front of the head: in the second stage, according to Burmeister, the eye has become double, but the two are as yet simple; they are now situated posteriorly to the second pair of antennæ: in the third or pupal stage, they remain in the same situation, but have

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become compound, of great size, and are attached to the apodemes of the antennæ: in the mature and fourth stage, they have moved someway posteriorly, and again have become simple, of minute size, and are either confluent, as in the Lepadidæ, or tolerably far apart, as in the Balanidæ. It must not be supposed that the eye of the mature Cirripede is metamorphosed from the eye of the pupa, for such is not the case; the new eyes and old eyes being formed someway apart, and frequently both can be seen within the pupa (as in Alcippe, Pl. 23, fig. 16) at the same time. It is scarcely possible that the eye of the larva in the first stage, can be changed into the double eyes of the second stage; though these latter may possible be multiplied into the eyes of the pupa, as both continue to occupy nearly the same position.*

Mouth, thorax, limbs, abdomen.—I have nothing to add regarding the mouth, except to confirm my former account; viz., that it is functionless, consisting merely of crests, which project inwardly between the gnathites of the young Cirripede, and of a shrivelled closed tube representing the œsophagus. In fact the mouth is a model of the outside of the mouth of the young Cirripede. I may remark that some little way beneath the membrane answering to the labrum, a pair of ligamentous apodemes, the use of which I do not know, slightly penetrate the body. The degree of prominence of the mouth varies, but it is far less than in the mature animal. On the limbs I have nothing particular to add: the drawing of the first pair of legs (Pl. 30, fig. 5) is, I think, very accurate: I observed all the spines here figured, on the corresponding leg of the pupa of Balanus Hameri. The five posterior pairs of legs differ only in the outer ramus having five plumose spines, instead of four, and one short simple spine at the exterior angle, making six alto-

* Zenker, in his 'Physiological Remarks on the Daphnidæ,' ('Journal of the Microscopical Society,' 1853, p. 274), speaks of a "tripartite azygous eye" as common amongst Crustacea, and as occurring "in conjunction with the aggregated eyes in Artemia, Argulus, &c.; but as appearing regularly in all the Branchiopoda and Siphonostomata as the earliest visual organ. Hence I conclude that this azygous eye is the homologue of that single eye which appears in the earliest larval stage of Cirripedes; and that the compound eyes of the cirripedial pupa, answer to the aggregated eyes of Artemia and Argulus, &c., with the difference, that in these latter genera the single eye is retained. See, also, Von Siebold, 'Anatomie Comparée,' tom. i, p. 435.

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gether. The legs, in their natural position (fig. 2), have only the terminal segments of their two rami directed posteriorly; and as a consequence the spine (close to i in fig. 5), borne on the penultimate segment of the outer ramus, is directed in the same line with that segment and with the pedicel, namely, anteriorly, and at right angles to the natatory plumose spines. This short spine acts, I imagine, as a defensive weapon; it has been omitted in fig. 2. Of the thorax I need not give, from my notes, any more details. The abdomen (fig. 6) is similarly constructed, as far as I have seen, throughout the order, with the exception of Alcippe (Pl. 23, fig. 17), in which it is composed of only one segment instead of three. In this genus the caudal appendages likewise consist of only one segment, with very short spines. In the pupa of Balanus balanoides, the three spines borne on each caudal appendage are very much more unequal in size than in the pupa of Lepas australis, although in the latter (fig. 6) the inner spine is considerably thicker than the two outer. Whether the three segments of which the abdomen is composed, are the three anterior or three posterior, of the normal seven segments, I know not: on the view that they are the three posterior segments, I presume, according to analogy, that the caudal appendages are borne on the penultimate segment, and that the ultimate segment is here quite aborted.

On the internal viscera I have nothing to add. The cement-duct is represented in Pl. 30, fig. 2, , on the near side, running into the antennæ; and I repeatedly traced it, for the duct is very strong, as far as the disc segment; at the other end it joins the cement-gland (t) on the same side of the body. This cement-gland is proved, by the clearest series of facts, to be converted into the incipient ovaria and ovarian cæca. The cement-glands in the older pupæ could be traced as far as the cæca of the stomach, exactly where the ovaria lie in the mature animal; but in some young pupæ, they extended further posteriorly, past the mouth, between the outer and inner membranes of the overlapping carapace. I have faintly shown the course of the stomach, with its two cæca at the upper end; the anus lies between the caudal appendages, at the extremity (above ) of the abdomen. At

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this age there is no trace of the vesiculæ seminales, so conspicuous in the mature Cirripede.

Young Cirripede, whilst within the pupa.—I repeatedly succeeded in dissecting the young Lepas australis out of the pupa; and by the previous action of boiling potash, and by a strong light, I was enabled to make a camera sketch (Pl. 30, fig. 2) of the relative positions of their several parts. The young Cirripede is drawn very faintly, and is best seen by holding the plate in the same position with the mature animal, of which a section is given in my volume on the Lepadidæ, Pl. 9, fig. 4. I may just notice how complicated are the membranes in a longitudinal section taken at this period: we have, 1st, beginning at the back, the horny tissue of the carapace or bivalve shell of the pupa; 2d, the primordial valve (z, in fig. 3) of the young Cirripede; 3d and 4th, two folds of corium; 5th, the membrane of the sack of the Cirripede; 6th, the membrane of the sack of the pupa; 7th, the outer tunic of the thorax of the pupa; 8th, the outer tunic of the thorax of the young Cirripede; 9th, the corium lining the latter membrane; and these nine membranes would be repeated on the opposite side of the section, if it were taken through either side of the shell or carapace, bordering the orifice.

After the exuviation of the outer membranes of the pupa, certain pre-existing coloured marks in the corium, such as those round the eyes and round the acoustic orifices, along the ridge of the back and on the borders of the orifice, &c., are still retained by the young Cirripede, either temporarily or permanently; so that the correspondence of part with part of the external surface admits of no doubt. Moreover, the three terminal segments of the antennæ are invariably retained by the young Cirripede, though in a functionless condition, and into them the outer membrane of the body, and an important organ, viz., the cement-ducts are still prolonged; hence these prolongations must be considered as aborted antennæ. Again, we have seen that the mouth of the young Cirripede is formed under the rudimentary mouth of the pupa, with the new œsophagus, round the old œsophagus, leading into the same alimentary canal. The twenty-four extreme tips, likewise, of the six pairs of biramous

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cirri of the Cirripede are formed within the twenty-four extremities of the six pairs of biramous, natatory legs of the pupa. Consequently, in the Cirripede and pupa, thus far, part corresponds with part, notwithstanding that new eyes are formed posteriorly to the old eyes, and new acoustic organs in a quite different position from the old ones; but now we come to a most important diversity in the metamorphosis, or rather to follow Professor Owen,* in the metagenesis, of the young Cirripede. Although, as just stated, the extremities of the cirri are formed within the legs of the pupa, yet, from the great length of the cirri, they occupy more than the whole of the thorax of the pupa; so that the thorax of the young Cirripede is not formed within the pre-existing thorax of the pupa, but within that part of the pupa, (homologically a portion of the first three cephalic segments), which lies anteriorly to the thorax. As a consequence of this, the pedicels and lower portions of the cirri, the segments of the thorax and its dorsal surface, all come to occupy a position at nearly right angles to that of the corresponding parts in the pupa: this is shown in Pl. 30, fig. 2. And as a further consequence, (and this is the more important point), the sack, which both in the young Cirripede and pupa is formed by the overhanging and produced portion of the carapace, and which is internally lined by a reduplication of the membrane of the thorax, is necessarily, owing to the changed position of the thorax, altered in extent and carried much further; namely, from extending merely parallel to the longitudinal axis of the pupa (from b to ), it is now in the young Cirripede, in addition, carried (to ) almost quite across the inside of the animal. Hence it comes that the young Cirripede is, as I have said in my former volume, internally almost intersected; and its body remains attached only by a small space, (see the broken line, round a and b in Pl. 25, fig. 1, of a Balanus with the shell, &c., removed from one side), to the sternal or ventral, inner surface of the carapace,—the carapace being modified either into the capitulum and peduncle, or into the shell with its operculum and basis. As a still further consequence of this change of

* 'Parthenogenesis,' pp. 13 and 26.

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position of the body of the young Cirripede within the body of the pupa, the alimentary canal becomes shortened to fully half its former length. At the same time, the interspace between the mouth and first pair of legs of the pupa, (consisting of the seventh and eighth segments of the archetype), is quite lost in the Cirripede by coalescence. The final cause of the thorax of the young Cirripede not being developed within the thorax of the pupa, probably is, that the cirri may be formed of considerable length, so as to be immediately enabled to seize prey; and that the thorax, which supports the cirri (and this probably is even more important) should be as free as possible within the sack, so as to aid the captorial action of the cirri.

After these remarks, more especially with regard to the formation of the sack, if any one will look at the sectional drawing of a pedunculated Cirripede in my former volume, or of a sessile Cirripede (Pl. 25, fig. 1) in this present volume, in which latter the shell adds to the complexity, he will perceive the cause of the extreme difficulty in understanding the relative position of the parts throughout the whole class. Even after I had discovered that the prehensile antennæ of the pupa might always be found in the centre of the basis or surface of attachment, and which fact, it might have been thought, should have convinced me that this was the anterior end of the whole animal, yet still I fancied that the prominent mouth represented the entire head, and that the shell was something quite distinct. It is clear that others have been equally perplexed; for that which is the anterior end in the eyes of one naturalist, is the posterior end in the eyes of another; so with the dorsal and ventral surfaces: one naturalist considers the peduncle of the Lepas as the abdomen; another considers it as a pair of metamorphosed, thoracic limbs, &c.! The probable position of the segments of the body of a mature Cirripede, in relation to the three anterior cephalic segments, or carapace, is shown in the diagram (Pl. 25, fig. 6) of the supposed position of the mature Proteolepas within its pupal envelopes. Here, in the diagram, the two segments immediately succeeding the mouth (c), which are the seventh and eighth of the archetype, (for the mouth consists of three segments, and all in front

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of the mouth of three other segments), have come to adhere by their dorsal surfaces to the internal surface of the carapace,—that is, of the first three segments, which ought of course to have stood quite in advance of these two segments, and these two segments again ought to have stood in advance of the mouth. The mouth is directed posteriorly, instead of from the body; and the three segments of which it is formed (closed at their anterior end by the labrum), and are very small compared to the relatively monstrously great, three anterior cephalic segments, composing the carapace. To place the segments of the body of Proteolepas in proper sequence, in respect to those of the carapace, and in accordance with the sequence of the archetype Crustacean, it would be necessary, by seizing the extremity of the abdomen (a), to tear the two segments succeeding the mouth from their dorsal attachment, as far back as the basal margin of the labrum; and then pull them till they stood posteriorly to (or in the diagram, above) the mouth; which latter part would, by the same movement, be made to project out at right angles to the ventral surface, and would then be preceded only by the first three, great, confluent segments of the head, which being produced backwards, form the carapace. All that has just been said on the position, in Proteolepas, of the segments of the body in relation to those forming the carapace, I believe to be applicable to all ordinary Cirripedes, with this difference, that in the latter, after the metamorphosis, the two segments succeeding the mouth quite disappear on the ventral surface, and dorsally are either aborted or have coalesced with the adjoining segments.

When the due time for the act of metamorphosis has arrived, the pupal carapace splits along the dorsal ridge, and is cast off, together with the acoustic sacks, the basal segments of the two antennæ, and the great, black, compound eyes, hanging to the UU-like apodemes. The three terminal segments of the antennæ invariably remain cemented to the surface of attachment. The exuviæ usually continue for a time united to the cemented antennæ, but are finally washed away. Besides the split along the dorsal ridge, the

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carapace separates, all round the orifice, from the delicate tunic lining the sack and investing the thorax and natatory legs of the pupa; for these membranes are not moulted for some considerable time afterwards. Hence all these inner parts retain for a period the appearance and structure of the natatory pupa, whilst the exterior resembles, in every respect, a fixed and perfect Cirripede.

In my former volume, I have insisted on the important and curious results which ensue from the eye-apodemes penetrating so deeply into the body (see Pl. 30, fig. 7, in which the proportions are more correct than in fig. 2), with the eyes attached exteriorly to their outer arms; for as these apodemes have to be ejected, the external membrane of the young Cirripede (Pl. 30, fig. 2) has to be formed in a deep fold or arch over them, and consequently the membrane on the sternal surface is formed considerably longer than on the dorsal surface. From this it follows, when all the membranes are free and are stretched fully out after the moult, that the whole animal, posteriorly to the cemented-down surface, turns vertically up, and assumes its normal position at right angles to the surface of attachment, and to that which it held in its pupal condition; for the pupa always adheres with its sternal surface parallel to the surface of attachment. A young Lepas, which has just moulted its pupal carapace, and has assumed its proper vertical position, with the cemented antennæ and the surface of attachment remaining as before, is shown at fig. 3, but is drawn on a smaller scale than the pupa fig. 2, out of which it may be supposed to have been excluded. In this fig. 3, it may be observed that the natatory legs and caudal appendages of the pupa have not as yet been moulted. The fact of the stretching out, in the young Cirripede, of the fold of membrane, which in pupa, just before the metamorphosis passes over the apodemes and eyes, is well shown by three darkly-coloured bands in the corium, which in the pupa are curled, but after the moult, are stretched straight out on the peduncle of the young Lepas.

The pupa, and consequently the young Cirripede, from being attached at first by the antennæ, does not adhere by the actual anterior extremity, but by the sternal surface near it;

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the anterior extremity, however, soon becomes cemented down, and afterwards, in ordinary cases, ceases to grow. In Cryptophialus, however, and in certain genera of the Lepadidæ as Alcippe, Lithotrya, and Anelasma, the anterior or basal extremity does continue to grow, and is not cemented down, and therefore comes to be prolonged beyond the original point of attachment; in order to allow of this, the surface to which the Cirripede is attached has to yield, apparently simply to the pressure exerted in the case of Anelasma, but in the three other genera, to the rasping action of the roughened surface of the extremity of the peduncle.

When after a period the pupal membranes of the sack, thorax, and natatory legs are moulted, the cirri of the young Cirripede are curled up, and its thorax is raised towards the orifice, and we have the animal in its ordinary position, and perfect with the exception of a few parts to be further developed or modified. For, instead of calcareous valves, we have at this period only the so-called primordial valves, composed of chitine; and in the case of Lepas australis, some minute spines and some coloured marks on the peduncle, which soon disappear. The muscles, which enter the three terminal segments of the antennæ in the pupa, have to be absorbed and converted into ligamentous threads. In Lepas, the labrum has to become bullate; and the cæca have to increase in number round the upper end of the stomach, and their dark colour and that of the whole alimentary canal has to disappear or be much weakened. The filamentary appendages at the bases of the cirri, which generally contain some of the testes, have to be developed. The probosciformed penis, which at first equals only the pedicels of the posterior cirri in length, and is apparently imperforate, has to increase greatly in length. The testes and vesiculæ seminales have to be formed. And lastly, and this is a more important point, the two gut-formed cement-glands (or incipient ovaria, t, fig. 2, Pl. 30) which, at the period of the moulting of the carapace and eye-apodemes, and when the whole animal was upturned, came to occupy, together with the cement-ducts (), their normal position , i. e. nearly parallel to the sternal surface, now undergo further changes. Their upper and posterior ends lying near

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the cæca of the stomach, increase in size, but retain nearly the same character, and thus form the two true ovaria; their middle parts become emptied of their cellular contents, and are converted into the two simple ovarian tubes; and their lower ends branch out, inosculate, and form the inextricable mass of ovarian tubes and cæca. The points of junction on each side between the two cement-ducts and the newly branched ovarian tubes, become now developed into the two cement-glands. The cement-ducts, which continue throughout life growing, either still enter the old antennæ and there pour out the cement-tissue, or they pour it out through special orifices formed for this purpose in the lower part of the peduncle. The changes, supervening during the metamorphosis, in the ovaria and in the cementing apparatus, here described, I have no doubt are general throughout the Order.

I have above alluded to the primordial valves; these are beautiful objects when viewed under a high power: they are composed of chitine without a trace of calcareous matter; but prefigure in shape, size, and direction of growth, the shelly valves soon to be formed under and round them. They are composed of an outer membrane, with its margins separated by yellow thickened rims from the membrane uniting the several primordial valves together; and this outer membrane is underlaid by a single layer of generally hexagonal, thickish cells (Pl. 30, fig. 3 a), varying from 1 to 2/6000th of an inch in diameter. These cells seem to contain a nucleus; and they are at first separated from each other by clear interspaces. If a specimen be taken, only a little before the formation of the calcareous valves, one or more layers of membrane, marked by an hexagonal reticulation, can be separated from the lower surface of the main hexagonal network. It is a singular fact, that in those genera in which there are several valves, the primordial valves occur only on five, namely, on the two scuta, two terga, and the carina; and these are the most persistent valves in the several genera. The other valves are prefigured only by brownish membrane, without the hexagonal tissue. In the mature Lepas, the membrane connecting the several shelly valves is not moulted, but dis-

9                    

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integrates; in the primordial valves, however, which stand far separate from each other, this membrane is moulted: and immediately after the first moult, the first layer of shell appears under and a little way beyond each primordial valve; shelly matter likewise appears, at least in some cases, between the cells of the hexagonal tissue. The young shelly valves are connected together, at each successive moult, by narrower strips of membrane, till, in the case of Lepas, the valves when mature come to touch each other (Lepadidæ, Pl. 1, fig. 5). The primordial valves are often preserved for a long time on the umbones, or centres of growth of the five valves, on which they occur, in the same manner as the larva-shell is sometimes preserved on the apex of certain spiral molluscs. Had not Cirripedes gone through so many and such complicated metamorphoses, this last state, when furnished only with primordial valves and with several internal organs only partially or not at all developed, would have deserved to have ranked as a special stage, and not as merely subordinate to the last or pupal condition.

In the Balanidæ, or sessile Cirripedes, the young animal, immediately after the metamorphosis, or still better if dissected out of the pupal carapace, as I succeeded in doing with Balanus balanoides, may be said to be pedunculated; for it is attached by a little disc of cement closely surrounding the antennæ, the rest of the membranous basis forming an almost semi-globular, flexible peduncle. The valves, at this the earliest period, are all membranous, and do not overlap each other. In the Balaninæ they do not present the peculiar structure of the primordial valves of the Lepadidæ; but in the Chthamalinæ in Chthamalus, I saw traces of this structure. Calcareous valves are soon formed under the membranous valves. The opercular valves, at this early period, are much larger than the valves or compartments of the shell, which are only four in number, for the carino-lateral compartments are not yet formed. The compartments from the first are surprisingly strong, and have their alæ already formed and overlapped by the adjoining compartments; but of the radii there is as yet no trace. The four compartments form a narrow but nearly circular hoop, which, from its relatively large diameter;

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tends to draw down the upper or posterior end of the animal, now forming the opercular valves; and as the basis soon becomes throughout cemented to the surface of attachment, the young Cirripede is much depressed. Soon the opercular valves are drawn a little way down within the shell, becoming attached to the sheath, instead of, as at first, to the very summits of the compartments. In regard to the changes which take place in the shell, in the number of the segments in the cirri, and in the number of spines borne on these segments, &c., during the continued growth of the animal, as they are chiefly important for the identification of the species, I will here refer to a discussion on this subject under the head of the Genus Balanus.

On the Homologies of the Carapace and Shelly Valves.—In the pupa, the carapace is produced, not only posteriorly, but anteriorly, so as to cover the entire animal, with the exception of a narrow sternal surface (Pl. 30, fig. 4): in front it is notched, where the sternal surface terminates, and from this notch a faint line runs along the dorsal surface, separating its tergal elements. In the young Cirripede, after the metamorphosis, there is no trace of this medial dorsal suture, or of the wider sternal surface. Looking at the several genera of the Lepadidæ, the external covering of the whole peduncle and capitulum is so continuous and of so uniform a nature, that I think we must consider the whole as a carapace, of which the sternal borders have become completely confluent; formerly I was inclined to look at the capitulum alone as formed by the carapace, and at the peduncle as being composed of the two or three anterior cephalic segments, cased only by their own integuments. As far as can be discerned, the carapace in the pupa, and consequently in the Cirripede, consists only of the tergal elements of the segments; and this seems likewise to be the case with the carapace of the Podophthalmia. Until lately,* Prof. Milne Edwards doubted whether the carapace in the higher Crustaceans (to which I believe the carapace of Cirripedes must be compared) was formed by the backward production of the third segment,

* Compare 'Histoire Naturelle des Crustaces,' tom. i, p. 27, with 'Annales des Sciences Nat.,' 3d series, tom. xvi, 1851, p. 233.

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which bears the second pair of antennæ, or of the fourth, i. e. the mandibular segment; but from the distribution of the nerves, he now argues that it must mainly belong to the third segment. In Cirripedes, the course of the nerves leads to the same conclusion; for the whole shell, sack, and peduncle are supplied with nerves proceeding from the compounded ganglion, which belongs to the second and third cephalic segments.*

The whole of the head in front of the mouth, together with the carapace, is, as we know, formed of three segments; and each of these segments, homologically, ought to consist of eight elements; I recall to mind these facts, inasmuch as the transverse separation between the peduncle and capitulum in the Lepadidæ, and between the basis, the shell, and the opercular valves in the Balanidæ, might be thought to be connected with the separation of the three cephalic segments. So again, as in the Balanidæ the shell normally consists of eight compartments, these might be thought to be related to the eight elements of one or other of the three segments. But I see no reason for admitting this view; and in the case of the carina and rostrum, two of the most persistent and important of the compartments, they exactly cover the sutures which ought to separate the two tergal and two sternal elements of the segment. The valves, moreover, often form many more whorls than three, or the number of the true cephalic segments in front of the mouth; and in each whorl the valves tend to stand in tile-like or alternate order, with respect to those in the whorls both above and below, which would not be the case, if they were the eight elements of the segments.

For the true homologies of the sclerodermic plates, or shelly valves, with which the external covering of Cirripedes is so generally strengthened, we must, I believe, look to the carapace of the Podophthalmia. In these latter, we

* This conclusion is supported by the structure of Proteolepas: in this Cirripede there is not a vestige of a carapace, and as the whole of the animal in front of the mouth is almost utterly aborted, being reduced to a mere covering to the two cement-ducts, and as, on the other hand, the mouth with the mandibles, though peculiarly modified, is not at all aborted, there is a strong probability, that the abortion of the carapace is connected with the aborted state of the three anterior cephalic segments; and that the carapace in its origin is not any way related to the fourth or mandibular segment.

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find the carapace composed of sclerodermic plates, which, though closely joined and only occasionally separated by sutures, yet in their origin are distinct;* they tend, also, to be arranged in alternate or tile-like order. As the animal grows, the old sclerodermic plates, all joined together, are moulted, and new ones, also all joined together, of a larger size, are formed beneath. Now let us imagine the growth to be more gradual but yet periodical, and the new and larger sclerodermic plates, when formed under the old ones, to adhere firmly to them; the older plates would thus be prevented from becoming confluent, and instead of being all moulted together, as is now the case, they would be almost continually separated from each other, owing to the almost continuous increase in size of the new underlying plates. Consequently lines of splitting would run between the several plates, however numerous they might be, instead of there being, as now, a single line of splitting extending down the back. In fact, we should have the identical manner of growth of the shell or carapace, which occurs in Cirripedes. It is on this ground, and from the several points of homological resemblance incidentally mentioned in the last few paragraphs, that, in the early part of this Introduction (p. 13), when discussing the whole class, I stated that I believed that the carapace of Cirripedes presented more real resemblance with the carapaces of the Podophthalmia, or higher Crustacea, than with those of the lower Crustacea, though in mere shape they more nearly resembled the latter.

Cementing Apparatus (Plate 28.)

I have already (p. 128) given an account of the manner in which, in the pupa of Lepas, the cement-tissue escapes from the prehensile antennæ, and of the structure of the cement-ducts, and of the cement-glands or incipient ovaria; and likewise of the changes by which these organs assume their ultimate form in the mature Cirripede. In my former volume, on the Lepadidæ, I described the cement-glands and the cement-tissue in several genera,

* 'Annales des Sciences Naturelles,' 3d series, tom. xvi, pp. 233, 236, 237.

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and I have there shown (singular as the fact is) that the two cement-glands, with their contents, actually consist of ovarian tubes with their contents (for there seemed to be a relation in the state of fulness in both) in a modified condition. In the Balanidæ, I am not able, from the difficulty of the dissection, to confirm these conclusions, excepting in so far that the tubes on which the cement-glands are formed, run into the mass of ovarian cæca; but, I may add, that in the abnormal Proteolepas, belonging to another Order (see the section, Pl. 24, fig. 1), nothing could be plainer than that the membrane of the ovarian sack (b) formed the cement-ducts, and that their cellular contents, which within the sack (a) were in process of conversion into ova, within the ducts were converted into the cement-tissue. This cement, by some unknown power, travels down the ducts, and debouches at the antennæ.

In the Lepadidæ, there are only two cement-glands, which are situated high up in the midst of the ovarian cæca, with one cement-duct proceeding from each: both the glands and ducts increase in size with the age of the animal:* the cement issues either permanently from the prehensile antenna, or, after a short period, through apertures in the peduncle, arranged irregularly or in straight lines,—the last formed apertures being furthest from the central and basal point of the peduncle. In the Balaninæ, on the other hand, at each period of growth, a pair of new cement-glands is developed, larger than those last formed, and making, with the older glands, a chain, connected together by what I have called the cement-trunk. The cement-trunk consists of a tube, which generally becomes enlarged just before entering each gland. The glands, the cement-trunk, and cement-ducts, all adhere to the basal membrane or basal shelly plate. Each gland gives rise to two cement-ducts, these often bifurcate, and sometimes repeatedly bifurcate and inosculate before pouring out their contents round the circumference of the basis; and sometimes they all first enter a circumferential cement-duct. The probable cause of the

* I had some slight reason to suspect in Pollicipes that new cement-glands were successively formed: this is more probable in this genus than in the others, inasmuch as it is the most nearly related to the Balanidæ.

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greater complexity of the cementing apparatus and of the greater number of the excretory orifices in the Balanidæ, compared with the Lepadidæ, is that the entire surface of the broad basis, which answers to the whole peduncle in the Lepadidæ, is firmly cemented down to the supporting object, instead of merely the basal end of the peduncle. The cement issues either in a cellular condition, or more commonly as a fine network, which, at a short distance from the orifices (Pl. 28, fig. 4 a, z), becomes so fine as to form a sheet or layer: I may here recall the fact, that in the cement proceeding from the disc of the antennæ, in some species of Lepas, a similar structure was observed. The cement itself presents the same transparent, brown, laminated, structureless appearance, and the same chemical reaction, as described in my former volume. The cement has the capacity of occupying and filling up all inequalities in the supporting surface; I have seen it, when spread over an encrusting Flustra, present an exact model of every cell; in the case of Coronula, it seems, as we shall immediately see, to have the power of penetrating into, and even almost blending with the epidermis of the supporting Cetacean. The last-formed cement-glands and cement-ducts present a delicate and transparent appearance, and contain cellular matter; whereas the old cement-glands, and sometimes the old cement-ducts, are filled with brownish cement, not acted on by boiling potash. The foregoing remarks are confined to the sub-family Balaninæ, for I have not been able to examine thoroughly the Chthamalinæ, and can only affirm, that in Chthamalus and Pachylasma the cement-ducts repeatedly bifurcate and inosculate, in the same manner as in the Balaninæ. I will now proceed to describe, in some detail, the cementing apparatus in the several following genera.

Coronula.—The cementing apparatus is here more simple than in any other genus of the Balaninæ, and I have studied it more carefully. The basal membrane of Coronula balænaris is figured in Pl. 28, fig. 1 a, and must first be described; its relation to the shell will hardly be understood without looking at the outline of the folded walls of this species, in Pl. 16, fig. 5. The basal membrane closes the central circular hollow, and is continuous with rays (not

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represented in Pl. 28) extending under the doubled walls and terminal transverse loops. It has eighteen concave sides, corresponding with the inner ends of the folded walls, for each of the six compartments is trebly folded. The membrane consists of successive, conformable slips (, ), bordered exteriorly by thickened yellowish rims, and internally overlapping (when viewed from the inner side) the few last-formed slips, and then thinning out. The membrane forming each slip is itself laminated. The middle portion, about 1/50th of an inch in diameter, is rather opaque, owing to the slips being so close together. Beyond this central part, the slips suddenly increase in size, but yet have a different shape from the 18-sided outline, which they ultimately assume: this difference is owing to the great changes in shape, as explained under the genus Coronula, which the shell undergoes, when the walls at first assume their folded structure. The walls are invested by longitudinally striated membrane (p, p, p, fig. 1 a), which turns in under their basal edges; and this membrane is united with the basal membrane, by what I shall call the circumferential slip (b), and which is shaded in fig. 1 a, simply for the sake of catching the eye. It is the circumferential slip of membrane which sends rays under the spoke-like folded walls: thin as it is, this slip is yet laminated, but is not bordered by thickened edges. The membrane investing the walls is, like the basal membrane, formed of successive slips with thickened edges, which overlapping (viewed from the inside) the last-formed slips, project beyond them, and so face the edges of the slips in the basal membrane; they are only obscurely indicated in fig. 1 a. The circumferential slip (b) lies over (as viewed from within) both the basal and wall membrane. This whole structure will, perhaps, be best understood by the sectional diagram (fig. 1 b), in which the letters (, ) show the slips of basal membrane; (p) the parietal membrane, coating the outside surface of the walls of the shell, not here represented; (b) the circumferential slip overlying both; and (z, z) the layers of cement, which may for the present be disregarded. In order to allow of the growth of the shell, the circumferential slip (b) periodically splits in the middle, all round,

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in a line exactly conformable to the edge of the last-formed slip of basal membrane; and likewise in straight, medial lines under the spoke-like (cut off in fig. 1 a) doubled walls. I have seen, under a high power, the line of splitting, very shortly after its formation, with the two edges ragged and near together, with an extremely narrow, new circumferential slip just formed, between and over the edges of the previously formed slip. What causes the circumferential slip to split so symmetrically, I cannot say: the opposed edges, after a time, become thickened, apparently from adhering to the underlying layer of cement, as will presently be described. The circumferential slip continues increasing in breadth till the period of its splitting arrives, by which time it has become much broader than the last-formed slip of basal membrane; and after the splitting takes place, the interior half towards the basal membrane, forms a new basal slip all round the basis, and the exterior half adds a new slip to the membrane investing the walls. This latter membrane being inflected under the basal edges of the walls, is, during the growth of their edges, drawn straight down, the newly-formed portion taking the inflected position.

In the sectional diagram, (1 b) the circumferential slip is not yet broad enough to split; when it has become so, it will split under the letter (b). The slips of basal membrane are, as may be seen in fig. 1 a, narrower towards the circumference; but the two or three last-formed slips, are out of proportion narrower than the others; and it is certain, from the comparison of the basal membranes of specimens of different ages, that these will afterwards increase in width.* I have seen no other instance, in Cirripedes, of growth in membranes, except at their extreme margins: I suspect that these last-formed slips are pulled, during the downward and outward growth of the shell, a little from over the last-

* In the case of one young shell, I found that the previously-formed circumferential slip must have split, long before it had assumed its proper and ordinary width; for the last-formed slip of basal membrane was of extreme narrowness, and would have to be considerably added to in width, whilst the new and narrow circumferential slip was likewise being added to in width. This slip of basal membrane, though so extremely narrow, had its own cement-ducts and glands.

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formed slips, new and larger laminæ being all the time thrown down, so as to prevent any fissure being formed. I also suspect that the gradual increase in width of the circumferential slip itself, is due to the opposed edges of the underlying and last-formed circumferential slip being dragged further apart from each other, new and wider laminæ of membrane being continually thrown down; the new circumferential slip being thus, also, all the time thickened, as well as rendered broader.

The central slip or rather disc of membrane, is 3/400ths of an inch in diameter; and this shows the basal diameter of the shell immediately after the metamorphosis. In the middle of this little disc I saw, in several specimens, the prehensile, pupal antennæ; I made out distinctly the ultimate segment with its bristles, and, as I believe, the disc-segment, which was 7/2000ths of an inch in diameter; but this portion was much obscured by the quantity of cement. When the corium is removed from the inner side of the basal membrane, the two chains of glands, extending from exactly over the antennæ in the centre about half way towards the circumference, are conspicuous. The cement-trunk, connecting the glands, is thin, and at the further end is always broken off, by the removal of the corium and overlying layer of ovarian cæca, into which the two cement-trunks enter; and without which removal, nothing could be seen. The two chains of glands form a very large angle, open towards the rostral end of the shell, as represented at fig. 1 c, much enlarged; by a mistake in fig. 1 a, the two have been drawn in a straight line. The cement-trunk increases in diameter in proceeding from the centre to the circumference, and the glands likewise increase in size, at the same time altering somewhat in shape. From near the lower side (the basal membrane being viewed from within) of each gland, two cement-ducts proceed, which pour out their contents beneath the basal membrane. The orifices of the ducts always exactly face the middle folds of the two lateral, and two carino-lateral compartments. In a full-sized specimen, there are from thirty-five to forty cement-glands on each side, always corresponding exactly with the number of slips of basal membrane, including the

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circumferential slip, to which the last-formed pair of glands and cement-ducts belong. In correspondence with the great number and narrowness of the central slips of membrane, so are the cement-glands towards the centre numerous and very small. All the glands, in the more central parts, consist of a mere transverse enlargement of the cement-trunk; but the exterior and larger glands, which are more closely packed together, are more globular or pear-shaped; and the two ducts (of which the one on the rostral side is considerably enlarged at its base) do not come out of the gland exactly at the same level. The trunk, connecting the glands, runs straight from one to the other. The ducts proceeding from the outer and older glands, on the carinal side, are much curved (Pl. 28, fig. 1 c). To give an idea of the dimensions of the several parts, I may state that the largest ducts were 3/1000ths of an inch in diameter, and the glands belonging to them nearly thrice as much, measured in the direction of the cement-trunk; on the other hand, some of the ducts from the small central glands had a diameter eighteen times less than that of the largest ducts. Towards the circumference, the ducts that proceed from the older and larger glands are piled one exactly over the other—the last formed being the topmost, and all are imbedded in the corium which overlies the basal membrane: this position of the ducts, one over the other (which could not be well represented in figs. 1 a and 1 c), is owing to their all debouching at the same exact point. But the ducts form the smaller and younger glands, when the shell had a different shape, are spread out, and are all attached to the basal membrane. Altogether, the basal membrane of Coronula, when well cleaned, and examined under a moderately high power, presents the most singular and elegant appearance.

We now come to the cement-tissue: this lies on the under or outer side of the basal membrane; it is not represented in figs. 1 a or 1 c, but only in the sectional diagram, 1 b, by the letters z, z: it presents its usual character and appearance, like solid glue or brown gum, but is obliquely laminated and sub-laminated: it forms a layer, much thicker than the basal membrane itself, being as

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much as .004 or .005 of an inch in thickness. It is, however, difficult to ascertain its thickness, from the singular manner in which it penetrates into and almost blends with the epidermis of the whale's skin; so much so, that for a considerable time I thought (not then knowing anything about the cement of Cirripedes) that this transparent horny substance probably answered to a corn on the human foot produced by pressure. But I soon observed that this horny substance certainly extended into and up the cement-ducts; and this fact first led me to the examination of the whole subject in the several genera of Lepadidæ and Balanidæ. It was not difficult to remove the cement-ducts, leaving small portions of the contained cement projecting freely up as points from the general surface of cement. The cement adheres slightly to the whole basal membrane, but chiefly to the yellowish rims or edges of the successive slips; and it is indeed this adhesion which, I believe, produces the rims; for the circumferential slip, when first split, had very thin ragged edges. The cement also extends under the spoke-like prolongations of the circumferential slip, and likewise some way up the sides of the walls.

The cement-glands, the trunk, and the ducts, except the two, three, or even four last-formed ones, are all filled with an apparently solid thread of transparent, brownish cement, differing in no respect from the cement under the central parts of the basal membrane. In one instance, in which the last-formed pair of glands and ducts had apparently been only just developed, they were so perfectly transparent that I could distinguish them only under certain lights, and I could not perceive any contents. The last-formed glands and ducts always appear very delicate, and include a tube of very delicate tissue, containing more or less of granular matter. The next succeeding pair of glands and ducts are always more opaque, and contain much more granular matter; which, in the next, or next but one, may be seen passing into the state of pale brown, transparent chitine. I have seen some most distinct instances, in which, in the same duct, the part towards the centre of the basis was filled with homogeneous cement, and the part towards the circumference with still plainly granular matter. In the

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successive circular slips of cement-tissue, lying attached under the circumferential slip and under the two or three succeeding slips of basal membrane, an exactly analogous series of changes is presented; as indeed might have been expected, as the slips of cement are absolutely continuous with the contents of the ducts. Moreover, if a vertical section be made across one of the last-formed slips of cement, it may sometimes be seen to be apparently in the act of separating into layers, with the lower layers more pulpy, elastic, and white than the upper layers, which are less coherent, and show as yet even still less the character of cement. The cement under the circumferential and adjoining slips, often presents a peculiar wrinkled appearance, in lines conformable with the outline of the basal membrane; but I do not believe that these are real wrinkles, though so like them; they seem to consist of sinuous threads, longer or shorter, sometimes slightly branched, crossing and interjoined, and composed apparently of faintly coloured cement. I suspect that these threads are formed by the union and subsequent drawing out of aggregations of that matter, which within the ducts is first granular, and then changes into cement; for at the orifices of the ducts these wrinkled threads sweep outwards in curved lines on both sides. The cement in these early stages adheres, with very little force, to the basal membrane; and with only a little more force to the underlying layers of cement; in fact, till it assumes the brown translucent appearance, like solid glue, it hardly seems to act as cement.

How the cement reaches the skin of the whale, will be best understood by referring to the sectional diagram (Pl. 28, fig. 1 b). When the circumferential slip of membrane (b) splits, a new circumferential slip will be formed over it, together with new cement-glands and ducts, and cement (z, z) will issue from four new orifices, and will extend on both sides of these orifices, till the ends meet and become united, thus forming a narrow, 18-sided, continuous, new slip of cement, with 18 spokes proceeding from it. I have not noticed lines of union in the cement of any one slip; but the matter forming each slip, certainly has proceeded from four distinct orifices. Seeing how per-

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fectly successive layers of cement often become blended together, lines of union of junction, could hardly be expected to be preserved in the same individual layer. When the circumferential slip of basal membrane splits, the underlying slip of cement, which we will call A, does not split, but becomes stretched, so that the newly-formed slip of cement, which we will call B, does not reach the skin of the whale. As the new circumferential slip of basal membranes goes on increasing in width, A continues to be stretched, but does not split, till at least another circumferential slip of basal membrane has been formed and has been split, and till B has been also stretched. By this time, the cement-tissue A has assumed its normal structure, and has the power of adhering to the whale's skin, which it has now reached, owing to the splitting of the under and older slips of cement. At the next period of growth, A itself will split, and B will touch the whale's skin and adhere to it; and this, also, will ultimately split. It results from this action, that the cement has a stretched, and sometimes even a fibrous appearance, with the lower edges of the layers, of which each slip of cement is formed, thinning out. I have before stated, that the two or three last-formed slips of basal membrane are formed at first too narrow, and apparently have to be dragged outwards, over each other; and it is perhaps owing to this circumstance, and to globules of cement having first adhered to the under surface of the slips of basal membrane, that these slips are studded beneath with parallel little vermiform bodies, sometimes of considerable length, and furnished with heads, all directed outwards. These tapering, vermiform bodies have a considerable resemblance to the threads before mentioned, which give the wrinkled, concentric appearance to the newly formed layers of cement, and have probably a closely analogous origin: in one case, indeed, it appeared as if some of these concentric threads were in process of being drawn out at right angles to their original course. Lastly, it should be observed, that as the exterior half of the membrane of the circumferential slip, after each splitting, is dragged down, and thus comes to invest the outer surface of the wall of the shell (the wall not being represented

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in the diagram, but standing where the letter (p) stands), so it must be with the cement, which thus likewise comes, in an unusual manner, to invest the outer surface of the folded walls of the shell, and attaches them to the skin of the whale,—which latter is always growing upwards, and tending to bury the shell.

Platylepas decorata.—This genus is closely allied to Coronula, and the cementing apparatus is essentially similar. In one specimen, I counted no less than forty-nine slips of basal membrane, each of which, of course, had its pair of cement-glands, and each of the latter its two ducts. The glands consists of a transverse enlargement of the trunk, as in the early stages of Coronula. Neither the glands nor the duct, when old, become filled up with cement, but only the main-trunk. The ducts are very delicate and thin; the larger ones being only 3/10,000 of an inch in diameter. The glands stand some way apart on the two cement trunks; and the latter, instead of being straight as in Coronula, are deeply serpentine; the glands are formed on each bend, so that, though all on one side are connected on the same trunk, they form a double row on each side of the basal membrane. The basal membrane (in the centre of which I distinctly saw the antennæ of the pupa) has six deep bays or excisions, corresponding with the midribs (see Pl. 17, 1 a, 1 d) of the six compartments; and the two ducts from each gland, on the right and left sides, debouch at the heads of the four lateral excisions, exactly opposite the midribs of the lateral and carino-lateral compartments. The later-formed glands, owing to all of them being situated some way apart from each other on the two cement-trunks, lie further from the centre of the basis than do the orifices of their ducts; hence the later-formed ducts are directed a little backwards, or from near the circumference towards the heads of the deep excisions.

Tubinicella.—The cementing apparatus is here less symmetrical; but this, I believe, is chiefly owing to the basal membrane being formed of successively larger discs (not slips) of membrane, thrown down not quite concentrically one over the other; each new disc of membrane seems to cover the last-formed cement-glands and ducts; and there are

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as many ducts and glands as there are discs of membrane, all adhering together. In one specimen, it appeared that normally there were four sets of cement-ducts, as in the allied genera of Coronula and Platylepas; but in other specimens, the ducts were distributed very irregularly. In one case the two cement-trunks extended parallel and close together, one of them terminating long before the other. I have given a figure (Pl. 28, fig. 3) of three of the cement-glands, removed from the basal membrane, together with their ducts. The cement-trunk (f f) seemed to be a little enlarged, and to be crossed by septa, as it entered the glands (h), but I could not make out this structure clearly enough to be represented. Whilst young, the cement-glands stand some little way apart from each other; and in the figure given of some of the last-formed glands, they are hardly separate enough. Each gland gives out obliquely, on one side, a cement-duct (c) which I traced in several cases to the margin of one of the discs of basal membrane, where cement issued from it; and on the opposite side, a tapering spur (b), varying in length, which may be called, and I believe really is, a rudimentary duct. Of these spurs we shall meet many instances in other genera. The duct (c) and the spur (b), close to where they entered the gland, in some specimens gave off, at about right angles, short blunt points, or rudimentary branches. This duct and spur correspond, I believe, with the two ducts in Coronula; but besides these, a duct (a) is given off from one end of the gland, from the surface opposite to that at which the cement-trunk enters. This duct (a) is very singular, from always forming a loop () with two spurs projecting from it: these two spurs occasionally spring from a common point: I have seen nothing like this structure in any other Cirripede. This duct (a) runs, like the duct (c), to the margin of its own disc of basal membrane, where it debouches. Besides these ducts, in the best specimen which I examined, there were two other sets of ducts, which were slightly zig-zag, and at each angular bend, a mere knob or point, or at most a short branch, was given off; but this branch seemed never to run to the margin of the basal membrane or to give out cement; whereas the main branch did give out cement. I was

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not able to trace these ducts to their glands. In these zig-zag ducts, and in the rudimentary points sometimes observed at the base of the duct (c), and likewise at the base of the spur (b), we see the first indication of that tendency to bifurcation, so strongly characteristic of the cement-ducts in all the genera, excepting those already described, which are allied to Coronula.

Chelonobia patula.—The cementing apparatus is here chiefly remarkable for the thinness and straightness of the main trunk, (f f, Pl. 28 fig. 2), and from the great distance at which the glands stand apart; had another gland been drawn, it would, on the scale here used, have stood exactly under the two upper, (c´ c´) in fig. 1 c. We here see that the trunk (f), before entering the gland (h), has an enlarged portion (g); this, I suspect, is a very general structure. Each gland gives out, on opposite sides, two ducts (a a, b b), larger even than the main trunk; and these ducts bifurcate repeatedly, and inosculate. By this inosculation it is not improbable that all four ducts, proceeding from the two glands of the same age, may be connected together; certainly the bifurcating branches from the same duct thus become repeatedly connected. For the first two or three bifurcations the ducts decrease very little or not at all in diameter; but nearer the circumference they become smaller. The ducts, also proceeding from the younger and smaller glands, are, of course, proportionably smaller. In one case I was able to count four bifurcations in the duct between the gland and the edge of the basal membrane. It follows from this structure, that the basal membrane, at each period of growth, is cemented down by cement issuing from several orifices; but we shall presently find that in other genera the cement proceeds from many more orifices. In fig. 2 there is represented, by the aid of the camera, a small portion (from the outer (a) to the outer (b) being 12/100ths of an inch in length) of the basal membrane, with all the several cement-ducts adhering to it, which I could distinguish, and drawn of their proper relative sizes; this figure also shows some of the bifurcations, but no inosculation happened to be included in the space here given; the basal membrane itself has not been represented. In taking

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a view of a considerable portion of the basal membrane, especially towards the circumference, some parallelism in the branches could be perceived; one set of branches tending to run in the direction of the ray of the circle, and the other set in the line of the circumference.

Elminius Kingii.—The cement-glands here resemble those of Chelonobia, but the trunk does not seem to be enlarged before entering the gland. The glands are situated rather far apart; and the chief peculiarity is, that the trunk connecting the glands is as tortuous as the track of a worm. Each gland gives out two ducts, which bifurcate repeatedly, and often inosculate, making, in parts, an hexagonal mesh-work: some of the branches do not debouch on the basal membrane, but terminate in blunt points. So numerous are the ducts, that the basal membrane may be compared to pieces of paper with the fine fibrous branching roots of some plant dried and heaped on it. Some of these ducts are very regularly jointed, and resemble a conferva,—an appearance which I believe is owing to divisions in the contained cement; other ducts are partially marked by little wrinkles, as presently to be described under Balanus. The cement, instead of, as heretofore, invariably forming a slip round and beneath the circumference of the basal membrane, here often forms little, independent, circular, and irregularly-shaped discs, each of which has issued from a single orifice. I may here add that in two species of Tetraclita I saw the cement-ducts repeatedly bifurcating, with some of the branches inosculating, as in Elminius and Chelonobia.

In Balanus balanoides, which, like all the Cirripedes hitherto mentioned, has a membranous basis, I could only make out an amazing number of bifurcating and inosculating cement-ducts, of very various diameters. The cement-tissue, on the under side of the basal membrane, generally consisted of little circular discs, on an average from 2 to 5 /2000ths of an inch in diameter; but there were also globules and short tortuous threads of cement. In some very much elongated and crowded specimens—in which, during the downward growth of the walls, the basal membrane had ceased to reach the surface of attachment, and being thus

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suspended had become, as viewed from the outside, deeply concave—the cement had apparently continued to try to reach the rock, and now hung down in the form of two thickish roots, some tenths of an inch in length. These roots were round, and tapered either to a fine or blunt point; one was doubled on itself, and so had become united; in the other, I could perceive five layers or sheets of the cement-tissue, one within the other; the innermost of these layers, which once, no doubt, formed the outside surface of the root, was only a quarter of its present length.

In Balanus tintinnabulum, the basis is calcareous: when its upper surface is cleaned, dried, and examined under a good light, the numerous larger cement-ducts can be seen, even by the naked eye, or under a weak lens, and present an elegant appearance. These larger ducts run in parallel lines from the two chains of glands towards the circumference. They are all encrusted with calcareous matter, and in the more central parts are hidden under it; at each period of growth, when the basis is added to round the circumference, it would appear that a layer of excessive tenuity of shell is thrown down over the whole surface, just in the same way as in Tubicinella, at each period, a new and larger disc of membrane was thrown down over the pre-existing membranes with their cementing apparatus. The cement-glands, in the middle of the basal plate, seem often to give rise to small abnormal depositions of calcareous matter. When the basis (it is best to take a young specimen) is slowly dissolved in acid, all the cementing apparatus is left uninjured, adhering to the delicate tissue which before existed in a calcified condition. Near the middle I saw the two antennæ of the pupa; and from them the two cement-trunks extended about half-way towards the circumference. These two chains of glands are often placed very irregularly, but they tend to form, as in Coronula, a large angle, open towards the rostral end of the shell. The glands, close to the old antennæ, commence abruptly, of rather large size: the later-formed glands, with their ducts, are in regular order larger than the younger ones, and stand much closer together. After immersion in acid all the glands and ducts appeared empty, instead of the older

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ones being, as in Coronula, filled with cement. In one case I counted on each trunk twenty-five glands, besides some smaller obscure ones close to the centre.

In Pl. 28, fig. 4 b, I have given a drawing of two of the cement glands: the cement-trunk (f f) is smooth and apparently cylindrical: it becomes enlarged (at g) before entering the gland: it seems even to be prolonged across the gland under the form of a narrow bar (not represented), which apparently serves to keep the two ends of the trunk, on the two sides of the gland, in their proper relative places and distances. The gland itself is an elongated bag (h), which properly lies exactly over the enlarged portion (g) of the trunk, but in the drawing has been purposely displaced: it gives rise, in the later-formed glands, to a sort of neck (see the upper gland), which is either so long as to deserve rather to be called a duct and which soon bifurcates, or is quite short (see the lower gland) and gives rise to two separate ducts. On the opposite side of these glands, there is a spur (m), of greater or shorter length, which is evidently a rudimentary duct, for in the younger glands it existed as a perfect duct. Moreover, the first-mentioned duct often gives off branches (), having an exactly similar appearance with the spur (m). The membrane of which the cement-trunk (f), with the enlargements (g), is composed, is smooth, but that of the glands and of all the ducts, presents a very peculiar appearance, which at first would be called scaled, but more properly perhaps notched,—each notch being apparently formed by a line of thickened membrane, extending obliquely round only a short portion of the tube, and indenting it. The ducts, which I measured, were between 1/3000th and 4/3000ths of an inch in diameter.

In fig. 4 a, I have given a drawing of the two chains of glands, but with only those ducts figured which proceeded from the last-formed pair of glands. The specimen here drawn was old; and it is rare to find the structure of the ducts so simple. From both glands* a neck or thick duct arises, which soon bifurcates; one branch runs direct into

* It should be observed that fig. 4 b ought to have been drawn with its present upper end downwards, to make it correspond in position with fig. 4 a.

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the circumferential duct, and the other (t) bifurcates again; of the latter, one branch unites with its fellow from the opposite gland, and then forming a single duct () enters, as do the two other branches, the circumferential duct. Thus, into the latter, five main ducts enter: the position of their points of entrance, with respect to the shell, varies considerably; but I think the five points tend to face the middle of the rostrum, and middle of the two lateral compartments on each side. In some other specimens, in which the ducts were nearly as simple, I observed that the neck or main duct at once divided into three branches, instead of into two, with one soon bifurcating; and on one side a rudimentary branch or spur was given off (above t), indicating a tendency to an additional bifurcation. In the later-formed glands, the ducts proceed only from the outer sides and form the ends of the glands furthest from the centre; but in the earlier-formed and smaller glands of the same individual, other ducts proceed from the inner sides, where in the older glands the spurs (m) are situated: moreover, in the younger glands, all the ducts bifurcate much oftener (how often I was not able to ascertain), before entering the circumferential duct; many of the branches, however, terminating in spur-like points. Now if we imagine twenty or thirty repetitions of the ducts given in fig. 4 a, (independently of the greater complication of the ducts of the younger glands), each a very little smaller than the other, and placed, with the main branches parallel, one over and within the other, we shall gain some insight into the wonderfully complicated structure of the cementing apparatus in this and many other species of Balanus.

I have as yet only alluded to the circumferential duct (i, i, Pl. 28, fig. 4 a): we have not hitherto met with this duct, but I suspect that the branches which in Chelonobia inosculate, and which seem to run nearly parallel to the circumference of the basal membrane, answer the same purpose of connecting the ducts together, and are, perhaps, strictly homologous. In this, and some other species of Balanus, the last-formed circumferential duct runs round the margin of the upper lamina of the basal plate, close to the basal edges of the walls; and as these latter have

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projecting longitudinal ribs, the duct curves a little round each rib; so that the whole duct is formed by as many short inwardly curved portions as the walls have ribs, or longitudinal septa. Between the basal extremities of these parietal, longitudinal septa, the extremities of the radiating septa of the basis project and enter; and along the crests of the latter, little branch-ducts (), proceeding from the circumferential duct, extend. In the basis, beneath the tubes formed by the just-mentioned radiating septa, there is a cancellated shelly mass (which, in fig. 4 a, was of unusual thickness), and along the crests of the branching ridges forming this cancellated mass, the sub-branches of the above branch-ducts () run; these soon become so minute as not to be distinguished by the highest powers, and thus form a sheet of cement, which attaches the last-formed zone of the shelly basis to the supporting surface. At what point the membrane forming any one duct ceases, the cement-tissue being alone left, I was not able to ascertain; but the lower parts of the reticulated slip (z, z, fig. 4 a) closely resembled the cement-tissue which surrounds the disc-segment of the pupal antennæ in Lepas australis. The circumferential duct, here and there, forms little loops, as may be seen in fig. 4 a: and often two branches, running along the crests of two adjoining basal septa, proceed from a common point of the circumferential duct. The cement itself, under different parts of the basis, appears as little separate discs, as threads, globules, and as a fine network, but most commonly as simple layers. As each thick zone of shelly matter is added round the basis, the exterior branches of the ducts, between the circumferential duct and the new layer of cement beneath, are fairly imbedded in shell, and are for ever hidden, without, indeed, acid be used for the dissolution of the calcareous matter: so, also, the pre-existing ducts and glands, and the main trunk, would all have been hidden, if the layer of calcareous matter, which, I believe, is thrown down at each period of growth over the entire surface, had not been of excessive tenuity.

I cursorily examined the cementing apparatus in Balanus galeatus, improvisus and crenatus, which have all calcareous bases, and belong to different sections of the genus; and

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the structure seemed to be essentially the same. In Bal. galeatus, I found the cement-ducts varying in diameter from 1/4000th to 1/10,000th of an inch in diameter. In B. improvisus, the cement-glands do not differ much from those of B. tintinnabulum; but the cement-ducts bifurcate often before entering the circumferential duct; and the little branches, which proceed from the latter, are very short, and almost immediately, owing to the thinness of the basis, blend into a slip of cement.

I hope to be excused for describing at such length, the apparatus by which sessile cirripedes are permanently attached to a supporting surface; for this is the great leading character of the sub-class, not hitherto observed in any other Crustacean.* It is not easy to overstate the singularity and complexity of the appearance of the basal membrane of a Balanus or Coronula: and when we consider the homological nature of the apparatus, the subject becomes still more curious: I feel an entire conviction, from what I have repeatedly seen in several genera of the Lepadidæ, both in their mature and pupal condition, and from what I have seen in Proteolepas, that the cement-glands and ducts are continuous with and actually a part of an ovarian tube, in a modified condition; and that the cellular matter which, in one part, goes to the formation of ova or new beings, in the other and modified part, goes to the formation of the cementing tissue. To conclude with an hypothesis,—those naturalists who believe that all gaps in the chain of nature would be filled up, if the structure of every extinct and existing creature were known, will readily admit, that Cirripedes were once separated by scarcely sensible intervals from some other, now unknown, Crusta-

* Rathke has described ('Acta Nova,' 1839, p. 147), in some siphonostomatous crustaceans, a pair of curious organs, which serve to secrete a substance that holds the eggs attached together in a mass to the parent's body: these organs Rathke has designated by a similar name to that which I have used, namely, the cementing organs or receptacles; they are distinct from the oviducts, but enter them near their external orifices. As in Cirripedes, the cement-glands and ducts are certainly continuous with an ovarian tube; and as they occupy a quite different position in the animal's body, these organs of Rathke, though in some degree analogous in function, must be homologically distinct.

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ceans. Should these intervening forms ever be discovered, I imagine they would prove to be Crustaceans, of not very low rank, with their oviducts opening at or near their second pair of antennæ, and that their ova escaped, at a period of exuviation, invested with an adhesive substance or tissue, which served to cement them, together, probably, with the exuviæ of the parent, to a supporting surface. In Cirripedes, we may suppose the cementing apparatus to have been retained; the parent herself, instead of the exuviæ, being cemented down, whereas the ova have come to escape by a new and anomalous course.

Affinities, Value of Characters, Variation.

Under the Order it has been stated that the Balanidæ, are, on the cirripedial type, the highest in the class; that is, they are the most complicated, but not (to use Professor Owen's term) by mere vegetative repetition. Amongst the Balanidæ, the first section of the genus Balanus may be taken as typical; here we have the structure of the shell extremely complicated, yet beautifully adapted for strength, and for the protection of the included body. The cementing apparatus is here, also, most complicated. I have divided the Balanidæ into two natural sub-families, the Balaninæ and Chthamalinæ, in accordance with certain differences in the structure of the shell and of the animal's body: that this division is natural, might almost be inferred from the one fact, that all the characters by which the Chthamalinæ differ from the Balaninæ, are those by which the former approaches the family of the Lepadidæ; moreover, certain anomalous characters in the Chthamalinæ, as the supplemental whorls of compartments in Catophragmus, and the presence of caudal appendages in this same genus and in Pachylasma, reveal this same affinity. The only objection which I can see to the separation of the sixteen genera into the above two sub-families, may be drawn from the degree to which they blend together; thus, as far as the shell is concerned, Chelonobia, in one important internal point of structure, tends to assume the character of

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the Chthamalinæ; and on the other hand, Pachylasma, a member of the Chthamalinæ, has a shell, which if not examined during its earliest growth, would be placed without doubt amongst the Balaninæ. But it fortunately so happens, that in no one character of the body does Pachylasma approach the Balaninæ more nearly, than do the other members of its sub-family; or Chelonobia approach, in the same respects, the Chthamalinæ. It is only in Chthamalus, of which the shell clearly places it in the sub-family bearing its name, that in some of the species, the less bullate labrum,—the larger palpi,—the lower teeth of the mandibles being laterally double,—and the lower segments of the third pair of cirri being thickly clothed, like the lower segments of the second pair, with bristles—all show that these species make an approach in structure to the Balaninæ.

It will be seen that I have divided the Balaninæ into two little groups, according as whether the branchiæ consist of one or of two plicated folds of membrane, and as whether or not the scutum and tergum are articulated together. I have been greatly tempted to follow Drs. Leach and Gray, who have separated the second of these groups, containing the genera Coronula, Tubicinella, Xenobalanus, and Platylepas, into the sub-family of the Coronulinæ. Certainly these genera have a peculiar aspect in common, and agree in being parasitic and imbedded in the skin of Cetaceans, as is the case with the first three genera, or in that of turtles, manatee, and sea-snakes, as in Platylepas. Though these genera possess several peculiar characters, yet I can find none common to all four, excepting their imbedment in the skin of Vertebrata, their double branchiæ, and their non-articulated opercular valves; and these I do not think of sufficient importance to serve for the separation of a sub-family; for in Chthamalus, one species has double branchiæ, one species has no branchiæ at all, and the other species have single branchiæ; so again in Chelonobia, the scutum having only a horny articular ridge, makes an approach to Coronula and its allies. I may further specify that the folded walls, a singular character common to Coronula, Platylepas and Xenobalanus, fails in Tubicinella; the open tubes and the

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imperfect outer lamina of the parietes towards their bases, are characters which fail in one species of Platylepas; the muscles running to the opercular valves being thinly spread out, and partially without transverse striæ, is also a character which fails in Platylepas; the simplicity of the cement-ducts partially fails in Tubicinella; and lastly, the existence of small intermediate teeth on the mandibles, fails in Xenobalanus: hence, I repeat, I have not thought it prudent to admit the sub-family of the Coronulinæ, though in many respects a very natural group.

The genera in the Balaninæ and Chthamalinæ are founded chiefly on the number of the compartments (the number being apparently due, as previously explained, to the fusion or abortion of certain of the eight typical compartments); and secondarily, on the nature and even form of the basis, and on the porosity of the walls. In Coronula and its allies, the non-articulated opercular valves and deeply folded walls come into play. As a justification for using these characters in distinguishing the genera, and even to a certain extent in separating the two sub-families, I must call to mind that the shell, with the basis, is not merely a dermal envelope, as amongst Molluscs, but actually consists of the first three segments of the head. The parts of the mouth and the cirri are of very little service in distinguishing the genera,—a singular fact, considering that most of the genera amongst the Lepadidæ could be distinguished by these organs,—though trifling details in their structure sometimes come in useful as specific characters. Balanus, with the sub-genus Acasta; Pyrgoma, with the sub-genus Creusia; Tetraclita, and Elminius, are genera of about equal value; though perhaps the two latter are rather more nearly related together than to the others. Chelonobia is more distinct; it shows some little affinity to the Chthamalinæ, and likewise to the four following genera. Coronula, Platylepas, Tubicinella, and Xenobalanus, are genera quite distinct from the foregoing, and from each other; yet, as we have just seen, palpably allied together. Amongst the Chthamalinæ, Pachylasma, Octomeris, and Catophragmus, are more closely related to each other than to the other two genera of the sub-family; yet Pachylasma,

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as far as the shell is concerned, leads into the Balaninæ, and Catophragmus into the Lepadidæ; Octomeris leads towards Chthamalus, and Chthamalus towards Chamæsipho.

Variation.—The discrimination of the species in most of the genera, offers very great difficulties. I cannot too strongly impress on any one intending to study this class, not to trust to external characters: he must separate and clean, and carefully examine the internal structure and form of the compartments, and more especially of the opercular valves. After considerable experience, when numerous varieties of a species have been carefully examined, the eye acquires a sort of instinctive knowledge, by which it can recognise the species, though the character cannot be defined by language; but I have found that no amount of experience with some of the commonest species, will save frequent and grave errors, as long as external characters alone are trusted to. Not only does every external character vary greatly in most of the species, but the internal parts very often vary to a surprising degree; and to add to the difficulty, groups of specimens not rarely vary in the same manner. After having given up several years to the study of this class, I must express my deliberate conviction that it is hopeless to find in any species, which has a wide range, and of which numerous specimens from different districts are presented for examination, any one part or organ,—which from differing in the different species is fitted for offering specific characters,—absolutely invariable in form or structure. I may in one respect even go further, and affirm, that, if in a species, any part or organ differs remarkably from the same part in its congeners, then if many specimens are examined, especially when collected from different districts, such part or organ will be found eminently variable. I may instance the antenniformed third pair of cirri in Chthamalus antennatus, the teeth on the posterior cirri in Acasta sulcata, the terga in Pyrgoma dentatum, the adductor ridge of the scuta in Pyrgoma cancellatum and in Creusia, and other such cases: hence it will not do to found a species on a slight, or sometimes even on a considerable difference, in any single point or organ. On the other hand, I am far from asserting, that if only half-a-dozen specimens of some

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rare species of Cirripede be brought from some one quarter of the world, characters beautifully defined may not be readily discovered. In determining what forms to call varieties, I have followed one common rule; namely, the discovery of such closely-allied, intermediate forms, that the application of a specific name to any one step in the series, was obviously impossible; or, when such intermediate forms have not actually been found, the knowledge that the differences of structure in question were such as, in several allied forms, certainly arose from variation,—for instance, in the case of two shells otherwise identical, one being longitudinally ribbed and the other smooth, a character which we know to vary,—but I have always used this argument from analogy with great caution. Finally, as in the large genus Balanus, there is an especial amount of variation, I have there entered in detail on this subject; and I hope that those interested in it, will refer to that discussion, which is almost verbally applicable to some other genera of the family, as Tetraclita and Chthamalus.

Rate of Growth. Exuviation. Powers of Repairing Injuries.—In my former volume I have shown that the pedunculated cirripedes grow rapidly; this is likewise the case with the Balanidæ. Mr. Stutchbury informs me that he has seen numerous specimens of Balanus tintinnabulum from 2 to 3 inches in height and from 5 to 6 inches in circumference (and this is nearly the full size which the species attains), on a vessel which had been to sea only during one year. At Coquimbo, in Chile, I have seen a specimen of B. psittacus 1.3 of an inch in basal diameter, and .8 in height, adhering to a chain that had been only six months under water. Poli, also, gives the case of some Balani (probably B. perforatus), which, in about four months, had attained a basal diameter of 1 inch, and a height of 1 1/6th of an inch. Balanus balanoides is a smaller species, and of slower growth; for the late Mr. W. Thompson, of Belfast, found that in three months from July 3d, certain marked specimens had increased from 2 1/2-3 lines to 4 1/2 lines, which is the usual maximum size attained in that locality. From other observations, Mr. Thompson believes that the extreme duration of life of this

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species is about two years: whether the other and apparently quicker-growing species, are shorter-lived, I have no means of judging.

In accordance with this rapid growth is the frequency of the periods of exuviation. Mr. Thompson kept twenty specimens of B. balanoides alive, and on the twelfth day he found the twenty-first cast-off integument, showing that all had moulted once, and one individual twice, within this period.* This frequency of exuviation, together with the durability of the cast-off integuments, explains the astonishing masses of exuviæ, which Mr. Peach assures me he annually has observed off the coast of Cornwall; they are most abundant in April and May, but he has seen quantities also in September; he could easily, as he tells me, have filled several quart-measures with them. The specimens sent to me consisted chiefly of Balanus balanoides, perforatus, and Chthamalus stellatus. The opercular membrane, with a narrow strip from between the two scuta, and another narrow strip from between the two terga, are moulted together, in connection with the more delicate membrane lining the sack, and investing the plicated branchiæ. This membrane, likewise, is continuously connected with that covering the whole body and its appendages. As I have stated under the Lepadidæ, the inner tunic of the œsophagus, of the rectum, of the olfactory pouches, and that which enters a little way into the acoustic meatus, and the apodemes of the maxillæ, are all moulted. On the cirri and jaws, new spines are formed with their upper ends enclosed within the old spines, but with their lower ends projecting inwards, beyond the bases of the old spines, and inverted like the fingers of a glove hastily pulled off. The membranes of the body, in the act of exuviation, split, I believe, only over the prosoma. How the neat separation of the opercular membrane, from all round the sheath and opercular valves, is effected, I do not fully understand; but it is, probably, analogous to the splitting of the thick carapace of the common crab. I suspect in Coronula, in which genus and its allies the oper-

* In Daphnia, Straus ('Mém. du Museum,' tom. vi, p. 151) found that the individuals moulted every five or six days.

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cular membrane is not periodically moulted, that the membrane lining the sack is not always thrown off at the same exact time with that of the body. In Chthamalus stellatus, in the act of moulting, the opercular membrane is the last part that separates from the new underlying membranes: I find that this species can moult when kept in a damp box out of water. The new membranes of the body, immediately after the exuviation, are not lax in any extreme degree. The exuviæ of the genus Chthamalus, and of some other genera amongst the Chthamalinæ, can at once be recognised by the divergence of the posterior four pairs of cirri: in the case of Chthamalus stellatus I have also noticed that the animal generally dies with these cirri in the same divergent position. Finally, I cannot doubt* that the Triton described by Linnæus was only the exuviæ of some Balanus (probably B. porcatus); Linnæus mistaking the probosciformed penis for the mouth of his imagined distinct animal.

I have seen a few specimens showing that when the shell has been broken it can be repaired; and this I believe is effected by the growth of a crest of corium between the broken edges, and the subsequent calcification of this crest. Mr. Stutchbury possesses a monstrous specimen of Chelonobia testudinaria, in which one of the lateral compartments on one side has not been developed. The cirri not rarely get cut off, but are, as it appears, soon repaired. I have observed a singular number of examples of the act of reparation in a group of the Australian Balanus vestitus. The manner in which the cirri are repaired seems to me curious: the cut-off end is closed by a rounded scale of yellowish chitine, and then the corium, in the four or five subjacent segments, separates from the external articulated membrane, which now serves only as a case or capsule. The tube of corium thus enclosed, with its contained muscles, shrinks a little, and soon can be perceived to be in process of

* Linnæus speaks of the included body (inhabitant as he calls it) of other Cirripedes, as a Triton; and this, I think, shows that Lesson's conjecture that the Triton was an Alepas cannot be correct; for Linnæus could hardly have supposed that a pedunculated cirripede inhabited another pedunculated or sessile cirripede.

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dividing into new and smaller segments,—in one instance ten in number,—which at the next exuviation would, no doubt, be invested with an external membrane, and be freely exposed. In another instance, the pedicel of a posterior cirrus had been cut off and subsequently closed; in this instance, a whole, immature, miniature cirrus, with the two rami, each having fifteen minute segments, was thus enclosed in what had been the single lower segment of the pedicel. I have seen several specimens of Balanus balanoides, as described under that species, with several of the cirri and the penis truncated; but I believe this was owing to monstrosity, which seemed particularly to affect the male organs of generation; for no reparation seemed to be in progress. In a specimen of Coronula, however, the penis appeared to have been really cut off by accident; it had been closed, by a scab, with concentric lines, like the articular rings on the penis itself; and within the case thus formed, the corium had healed, and had become pointed, but inverted; I presume that the point would, after another exuviation, have been everted, and its length thus increased.

Geographical Range and Habits.

With respect to range, the results arrived at have no particular interest, for the species are not sufficiently numerous; and, what is still more adverse, the genera, with unimportant exceptions, range over the world; so that there is no scale of differences, and it cannot be said that these two regions differ in their genera, and these two only in their species. In all the following remarks, I have trusted exclusively to my own specific identification; and have rejected all assigned localities which appeared from any cause to be doubtful. Sessile cirripedes are found in every sea, from lat. 74° 18´ north to Cape Horn. The area included between the north point of the Philippine Archipelago and the south point of Australia, extending on the right hand to New Zealand, and on the left to Sumatra,—an area, which, though including two distinct Cirripedial regions, is small compared with the surface of the globe,

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yet includes a greater number of species, especially of peculiar species, than the whole rest of the known world. This is, probably, in chief part due to the broken nature of the land, affording diversified habitats, and to much of the coast being rocky. Cirripedes, from requiring to be attached, cannot live where the shores and adjoining bottom are sandy or muddy or formed of moving shingle; hence, no doubt, it arises, that there is such a remarkable contrast in the great number of the species inhabiting the bold rocky western coast of South America, and the few species living on the sloping, and often sandy or muddy or shingly, eastern shores of this continent. Hence, also, I believe, it is that not many species have been brought from India. Coral-reefs are not favorable to Cirripedes, consequently but few are known to inhabit the islands of the Pacific Ocean. Where Cirripedes can live, though the species in no district are numerous, the individuals abound in infinite numbers: I have walked over the coast-rocks of the Falkland and Chonos Islands, of Chile and Van Diemen's Land, fairly encrusted over wide spaces with a continuous layer of Cirripedes, consisting of only two or three species; in the same manner as may be observed on many parts of the shores of Great Britain, and, I believe, of North America.

With respect to the effects of temperature on the range of Cirripedes, no genus (having more than one species) is confined to the torrid zones. Pyrgoma, from being always attached to corals, is, of course, ordinarily found in the hotter seas; but one species ranges from the Cape de Verde Islands in the torrid zone to the southern shores of England and Ireland. Tetraclita is not found in the colder seas, but is numerous in species and in individuals, on the southern shores of Australia and at the Cape of Good Hope. I may here add, that the two genera with the most confined ranges, are Chamæsipho and Elminius; the former has only two species, one inhabiting Australia, and the other the East Indian Archipelago; Elminius has four species, confined to the southern hemisphere, and inhabiting Australia, New Zealand, and South America. To return to the effects of temperature; in Mr. Dana's great work on Crustacea, an excellent chart is given, in which the isocrymal lines, or

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those exhibiting the mean temperature of the waters along their course, for the coldest thirty consecutive days in any season of the year, are given; and which lines Mr. Dana has shown are the most influential in governing the distribution of marine animals. At the isocryme of 68°, Mr. Dana divides the torrid and sub-torrid zones from the several temperate zones; and at 44°, the temperate from the sub-frigid and frigid zones; but as no Cirripedes are exclusively confined to these frigid zones, we may here disregard them. From Mr. Dana's* table of the areas of the torrid and temperate ocean-zones, on both sides of the equator, it seems that they are nearly as 337 to 278, in relative area; and consequently, he remarks, that the marine species in any class, if distributed equally over the two, would be one fifth more numerous in the torrid than in the temperate zones. Now of Cirripedes, taking all the orders, there are at present known 147 species; of these, 7 have doubtful habitats, leaving 140 for comparison. Of these 140, nearly one quarter, or 37, inhabit both the torrid and temperate zones, as above defined; 46 are found exclusively in the torrid, and 57 exclusively in the temperate zones; so that the temperate zones, though less in area, and having, proportionally, even a considerably lesser length of coastline, nevertheless have a preponderance in the number of species. But it should be borne in mind, that there are two great temperate districts, separated from each other by one great torrid district; and, inasmuch as the number of species in any region seems to depend in some degree on the isolation of the sub-regions, we might have expected (the other conditions now being, and the past conditions having been alike), that the two great temperate areas would have contained more species, perhaps doubly more, than the single great torrid area.

The proportional numbers, above given, are not very widely different, whether we take separately the Balanidæ, the Lepadidæ, or all together. Mr. Dana has shown† at length, that generally amongst the Crustacea, the species which he considers of highest rank, belong to the extra-

* 'Crustacea: United States Exploring Expedition,' p. 1476 (corrected).

† Ibid., p. 1528.

11                      

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torrid zones: there seems to me in all such cases to be some degree of vagueness in the attempt to determine which are highest or lowest, but I have already elsewhere stated that Balanus is, probably, the most eminently Cirripedial form, and exhibits in the strongest manner all the characters by which Cirripedes differ from other Crustacea; as this genus is the largest, containing 36 species, of which the habitats are known, I may state that of these, exactly one third, or 12, inhabit both zones; 9 exclusively inhabiting the torrid, and 15 exclusively the temperate zones. According to the proportions of the whole class, the numbers should have been 9 torrid, to only 11.11 temperate; so that evidently the genus Balanus (in one sense typical) inclines towards the temperate regions more strongly than does either the family or the sub-class to which it belongs.

With respect to the relation between the size acquired by the different species of sessile cirripedes, and the temperature of the localities inhabited by them, the genera Chthamalus, Tetraclita, and Balanus, alone can serve for comparison: in Chthamalus much the largest species is found in the temperate zone: on the other hand, the two largest species of Tetraclita are from the torrid zone, though one of them also sometimes ranges into the temperate seas: in Balanus, the largest species, and six other species having a basal diameter sometimes over two inches, inhabit the temperate regions; and two out of these seven species, flourish even in the Arctic seas; whereas, within the torrid zone, there are only three species with a diameter sometimes exceeding two inches, but two of these frequently become very large and massive; so that Balanus, judging from the size of the species, as well as from their range, does not require for its highest development the temperature of the torrid zones.

The greater number of the species of the Balanidæ have wide ranges, as might be inferred from the fact of between one third and one fourth of the total number inhabiting both the torrid and temperate zones; but it should not be overlooked, that those species, as Balanus tintinnabulum, amphitrite, improvisus, and, in a lesser degree, B. trigonus

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and Tetraclita radiata, which seem to range over nearly the whole world (excepting the colder seas), are species which are habitually attached to ships, and which could hardly fail to be widely transported. Indeed, it appears to me surprising, that such species as Balanus psittacus and eburneus, which often become attached to vessels, should still be confined, the one to Southern, and the other to Northern America. But some other Cirripedes, which I have never seen attached to vessels, have likewise immense ranges: thus Tetraclita porosa is found in every tropical and warmer sea, and Chthamalus stellatus ranges round the world in the northern hemisphere, and, along the eastern side of America, far south of the equator: Balanus spongicola, and Acasta spongites, extend from the shores of Britain to the Cape of Good Hope: Balanus lævis ranges from Tierra del Fuego to California. I may further remark, that the only two other species of Balanus, and the one Chthamalus, inhabiting Tierra del Fuego, are, also, found on the shores of Peru. But to show the powers of endurance in some species, I may specify the case of Balanus improvisus, which fluorishes on the coast of Nova Scotia, amongst the West Indian Islands, in Southern Patagonia, and near Guyaquil. Even more striking is the case of B. crenatus, of which I have seen specimens from latitude 74° 48´ north, from the West Indies, and the Cape of Good Hope! In these two latter localities, however, it seems to be rare, and may have been first transported to them from the shores of Europe, on the bottoms of vessels, to which it sometimes adheres.

The several species of Balanidæ live attached either to coast-rocks, or to objects at various depths, down to, as in the case of Balanus crenatus, 50 fathoms. Balanus balanoides sometimes adheres to rocks or wood so high up, that it is not covered by water during the neap tides. Mr. Thompson has informed me, that he once accidentally kept some specimens of this species out of water for seven days in a warm room, and that they were then quite lively. This species, is very easily killed by brackish water, as are some other species, whilst B. improvisus and eburneus can flourish in it; and at the Falkland Islands, I saw Elminius Kingii attached to rocks at the mouth of a fresh-water

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brook, so as to be covered by pure water during the ebb of each tide. Sessile cirripedes adhere to all sorts of objects, floating and fixed, animal and vegetable, living and dead, organic and inorganic. Chthamalus is, perhaps, more commonly attached to rocks than are the other genera. Living Mollusca are, I think, the most frequent objects of attachment: Mr. Cuming has remarked to me, that shells covered by an epidermis, as Patella, Haliotis, and Mytilus, are the greatest favorites. Acasta is always imbedded in sponges, or in the sponge-like bark of Isis; Pyrgoma and Creusia in corals; Chelonobia is attached to turtles, and one species to crabs or very smooth shells; Coronula, Tubicinella, and Xenobalanus, are imbedded in the skin of Cetaceans; and Platylepas in that of manatee, turtles, or sea-snakes.

If we attempt, with our present not very imperfect materials, to divide the globe into provinces, according to the amount of difference in their Cirripedial inhabitants, including all orders and families, and disregarding entirely, as I think we ought, all probabilities or conclusions deduced from the distribution of other tribes of animals, we find that the globe may be divided into the four following great provinces and one sub-province. I should premise, that in the following remarks and tables,* the species of Lepas, Conchoderma, Chelonobia, Coronula, Platylepas, and Tubicinella, are excluded, owing to their being attached to floating or swimming objects, and being consequently widely and irregularly distributed.

The first, or North Atlantic province, is that of Europe and the eastern shores of North America, from the arctic regions to lat. 30°: the island of Madeira, part of the north-west coast of Africa, and the whole Mediterranean being included. In this province (the above-named genera being excluded) we have 31 species, of which 22 are not found in any other distant quarter of the globe. As some few of these species range into the West Indies, I have not, on this account, excluded them from the 22 peculiar forms.

* As the number of Cirripedes in the whole class is not very great, I have given lists of the species in the four main provinces and in the one sub-province.

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Had I included the West Indies* in my first province, the total number of species would have been 42, of which 28 would have been peculiar. The coast of Brazil, even as far south as the Rio Plata, might, also, have been included, for I have not seen from it a single species not included in the above 42 West Indian species. So also, by adding a single species, might the west coast of equatorial Africa. The two coasts of South America and Africa, which face each other within the torrid zone, seem to be remarkably barren in Cirripedes. Europe has several more species than the United States, which is inhabited by only ten species, including even the probably imported Balanus tintinnabulum and amphitrite. Of these ten United States species only two are not found in Europe; and both these two range into the West Indies, and as far as the northern shores of South America, and therefore cannot be considered as peculiar to the United States.

I have formed my single sub-province for the southern extremity of Africa; for although I know of only 11 species from this comparatively short and uniform line of coast, yet I was not able to group these eleven in any of the main provinces: 5 of the species are peculiar. 1 Australian, 3 European and West Indian, and 2 almost universally distributed.

The second province includes the west coast of North and South America, from Tierra del Fuego to Behring's Straits: on this enormously long line of coast, only 22 species are known to exist, but of these no less than 15 are peculiar. Of these 15, four are not found south of the torrid equatorial region, and eight are not known to occur north of this same region; so that this long line of coast might have been divided into two sub-provinces, of which the southern would have been the most peculiar; but as eight species are found both north and south of the equatorial region, I have not made this sub-division. Two of the species occurring on the western coast of North America, seem to

* The total number of species which I have seen from the West Indies, is 19 or 20; of these, only 6 are peculiar to it, or 8, if the United States be likewise included, the other 12 or 14 species being found in other quarters of the world. Six peculiar species out of 19 or 20, has not appeared to me sufficient to institute even a sub-province.

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represent species found on its eastern coast, and in Europe; thus, Balanus glandula takes the places of B. crenatus, and B. cariosus that of B. balanoides. Not a single species, excepting a few which are also widely distributed over other parts of the world, is known to be common to the east and west coasts of the two Americas.

The third province is that of the East Indian Archipelago, and includes the Philippines, Borneo, New Guinea, Sumatra, Java, Malacca, and the eastern coast of India. Here we find 37 species, of which 24 are peculiar. I may remark, that I have received no species from Madagascar or the eastern coast of Africa; few from India, or from the coast of China; and I suspect, that on most of these coasts, only few exist. Probably our third province will hereafter be found to include the whole Indian Ocean.

The fourth province is that of Australia, including New Zealand: it has 30 species, of which 21 are peculiar. Had the temperate Australian coasts (i. e., those south of the isocryme of 68°) been alone considered, the number of the species would have been probably 25, of which 20 would have been peculiar,—that is, if we admit within the 20, several species which range from the temperate into the torrid zone, but do not extend beyond the Australian shores. Owing to the widely-extended ranges of most Cirripedes, no Arctic or Antarctic provinces can be said to exist.

To recapitulate the above results, bearing in mind that, although the total number of known existing Cirripedes is 147, yet that the habitats of seven are unknown, and that eighteen are excluded owing to their being attached to floating or swimming objects, so that there are only 122 species referred to in the following table:




Total number of species. Species confined to the province.
(1.)
First, or North Atlantic Province, to lat. 30° N. (If the West Indies had been included the numbers would have been 42 and 28) . . .

31 22
(2.) Sub-province of South Africa . . .
11 5
(3.) Second province, or West Coast of North and South America . . . . .
22 15
(4.) Third province, or East Indian Archipelago .
37 24
(5.) Fourth, or Australian province . . .
30 21

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The least prolific of these provinces contains 22 species, or between 1/5th and 1/6th of the total number of species, and the most prolific between 1/3d and 1/4th of this same number. In each of these provinces, it is remarkable that the peculiar species are very nearly two thirds of the whole of its inhabitants. These facts, I think, show that the above provinces are natural divisions of the world, as far as their Cirripedial inhabitants are concerned.

As Cirripedes belong to the great class of Crustacea, and as the distribution of the latter has lately been fully discussed by Mr. Dana, it may be worth while briefly to compare my results with his; more especially as they are so very different. I should premise, as perhaps accounting to a certain extent for this difference, that, owing to the wide range of many species, and the almost universal extension of the same genera, my provinces are founded merely on a certain proportion of the species, namely, two thirds, being peculiar or confined to a region of considerable dimensions: whereas, in the case of ordinary Crustaceans, the greater number of the species are distinct even in the sub-provinces, and the provinces are founded mainly on generic differences. Mr. Dana divides the surface of the globe into three great sections, or provinces, the Africo-Europæan, the extent of which is shown by its title; the Occidental, which includes both the east and west coast of both Americas; and the Oriental, including the Indian and Pacific Oceans, with the East Indian Archipelago, and Australia. Thus Mr. Dana entirely separates the Eastern shores of North America from Europe; whereas, as far as their Cirripedial inhabitants are concerned, they are most intimately allied, and form my first or North Atlantic province; and to this, as I have shown, even the West Indies, the coast of Brazil, and equatorial West Africa might have been added. It follows, from this similarity in the Cirripedes on the two sides of the Atlantic, and from their dissimilarity with those on the shores of the Pacific, that the east and west coasts of the two Americas form two quite distinct Cirripedial provinces; though, in the northern half, some connection is shown by a few representative species: on the other hand, Mr. Dana unites both sides of the whole American

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continent, into his single Occidental province. The South-African province is not brought out by Mr. Dana so prominently, as I have found necessary. Mr. Dana joins the East Indian Archipelago and Australia into his single Oriental province, and makes New Zealand, as a sub-province, apparently as distinct from Australia, as Australia is from the East Indian Archipelago: whereas I find that the Cirripedes of New Zealand clearly belong to Australia; and that the Australian Cirripedes, especially if the temperate shores be alone considered, are as distinct from those of the East Indian Archipelago, as from those of any other quarter of the whole world. I believe that the provinces deduced from the distribution of Cirripedes, accord better with the Molluscan provinces, than with those given by Mr. Dana for the rest of the great class of Crustaceans.

In the following tables, an asterisk means that the species is not found in any other distinct region of the globe. When found in one of the five provinces, a corresponding number, within brackets, is appended, to show in which province or sub-province it has been found.

(1.) FIRST OR NORTH ATLANTIC PROVINCE: Europe and the Eastern United States, from the Arctic Regions to 30° north latitude.

Balanus tintinnabulum . .
(1 to 5).


tulipiformis* . .
confined to Europe.


calceolus . . .
Europe and India.


galeatus*. . .
confined to North America and West Indies.


spongicola . . .
(2) and West Indies (?)


perforatus* . . .
confined to Europe, but possibly in the West Indies.


amphitrite . . .

(1 to 5.)


eburneus* . . .

confined to North America and West Indies.


improvisus . . .

Europe and North America and (3).


porcatus* . . .
Europe and North America.


crenatus . . . .
     ,,                     ,, W. Indies and (2).


balanoides* . . .
     ,,                     ,,


Hameri* . . . .
     ,,                     ,,

Acasta spongites . . . .
Europe and (2).


cyathus* . . . .
Madeira and West Indies.

Pyrgoma anglicum* . . .
confined to Europe, but ranges as far at least as the Cape de Verde Islands.

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Xenobalanus globicipitis*
confined to Europe.

Chthamalus stellatus . .
Europe and North America and (3 and 4).

Pachylasma giganteum*

confined to Europe.

Verruca Strömia . . . .
Europe and Red Sea.

  Spengleri* . . .
Madeira.

Pœcilasma aurantia* . .
      ,,


crassa* . . .
      ,,

Dichelaspis  Lowei* . . .
      ,,

Oxynaspis  celata* . . .
      ,,

Alepas   minuta* . . . .
Europe.


parasita* . . . 
Europe and Atlantic Ocean.

Anelasma   squalicola* . .
Europe.

Alcippe  lampas* . . . .
      ,,

Scalpellum  vulgare* . .
      ,,

Pollicipes  cornucopia* . .
      ,,
Here we have 31 species, of which 22 are not found in any other great region of the world.

(2.)
SUB-PROVINCE: Africa, South of lat. 30°.

Balanus tintinnabulum . .
(1 to 5).


Capensis* . . .



spongicola . . .
(1) and West Indies (?).


amphitrite . . . 
(1 to 5).


crenatus . . . . 
(1) and West Indies.

Acasta   spongites . . .
(1).

Tetraclita  serrata* . . .



rosea . . . . 
(4).

Chthamalus   dentatus* . .
also on West Coast of Africa.

Octomeris  angulosa* . .


Scalpellum  ornatum* . .

In this small region we have only 11 species, of which five are peculiar: Balanus Capensis and Tetraclita serrata, seem to be representatives of B. psittacus of S. America and of T. porosa of that and several other regions.

(3.) SECOND PROVINCE: West Coast of South and North America, from Tierra del Fuego to Behring's Straits.

Balanus  tintinnabulum . .
north and south of the equator (1 to 5).


psittacus*. . . 
south.


vinaceus* . . . 
   ,,


trigonus . . . . 
north and south (4 and 5).


lævis*. . .
          ,,


concavus . . .
          ,,            (4 and 5).


poecilus*. . . 
south.


improvisus . . . 
south (and north ?) (1).

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Balanus nubilus*. . . .
north.


glandula. . . . . 
north, and Southern Pacific Ocean.


cariosus*. . . 
north.

Tetraclita porosa . . . . 
north and south 4 and 5 and W. Indies).

Elminius Kingii*. . . 
south.

Chthamalus   stellatus. . .
north.


cirratus*. . . 
south.


scabrosus*. . . 
   ,,


fissus*. . . 
north and south.


Hembeli*. . . 
north.

Verruca lævigata*. . .
south.

Pollicipes   elegans*. . .
south and north.


polymerus*. . .
           ,,

Cryptophialus minutus*.

south.
Here we have on this long line of coast, 22 species, of which 15 are peculiar.

(4).

THIRD PROVINCE: Indian Archipelago (including the Philippines, Malacca, Borneo, Sumatra, Java, and New Guinea, and eastern coast of India).

Balanus tintinnabulum . .
(1 to 5).


Ajax*. . . . .



navicula * . . .



stultus . . . . 
and West Indies.


trigonus . . . . 
(3 and 5).


concavus . . . 
(3 and 5).


amphitrite . . . 
(1 to 5).


patellaris*. . .



amaryllis . . . . 
(5).


quadrivittatus* .


Acasta   lævigata . . . .
and Red Sea.


fenestrata* . . .



purpurata* . . .



sporillus* . . .


Tetraclita  porosa . . . . 
(3 and 5) and West Indies.


costata* . . .



vitiata . . . 
(5).


coerulescens . . 

Pacific Ocean.


radiata . . . 
(5) and West Indies.

Pyrgoma  cancellatum* . .



grande* . . .



milleporæ* . .



crenatum* . .



monticulariæ*


Creusia spinulosa . . . 

and West Indies.

Chthamalus
stellatus . .
(1 and 3).


intertextus* .


Chamæsipho scutelliformis*



Octomeris brunnea* . .


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Pœcilasma fissa* . . .



eburnea* . .


Dichelaspis Warwickii* .



Ibla Cumingii* . . . .


Scalpellum rostratum* . .



Pollicipes mitella* . . .



Lithotrya  Nicobarica* . .



truncata . . . 
and Pacific Ocean.
Here we have 37 species, of which 24 are peculiar to this province.

(5.) FOURTH PROVINCE: Australia (including New Zealand).

Balanus tintinnabulum . .
(1 to 5).


nigrescens* . . .



decorus* . . .



trigonus . . . . 
(3 and 4).


concavus . . . 
(3 and 4).


amphitrite . . . 
(1 to 5).


amaryllis . . . 
(4).


allium* . . . .



vestitus* . . .



imperator* . . .


Acasta  sulcata* . . . .



glans* . . . .


Tetraclita  porosa . . .
(3 and 4).


rosea . . . . 
(2).


purpurascens* .



vitiata . . . 
(4).


radiata . . . 
(4) and West Indies.

Elminius  plicatus* . . .



simplex* . . .



modestus* . . .


Chthamalus antennatus* .



Chamæsipho columna* . .

and Pacific Ocean (?).

Pachylasma aurantiacum* .



Catophragmus polymerus*



Alepas tubulosa* . . .



Ibla quadrivalvis* . . .



Scalpellum Peronii* . . .


Pollicipes  spinosus* . . .



sertus* . . .


Lithotrya cauta* . . .

Here we have 30 species, of which 21 are peculiar.

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Geological History.

The ancient history of the Balanidæ is a brief one. No secondary species has hitherto been discovered; in my monograph on the fossil Lepadidæ* I have shown that the negative evidence in this case is of considerable value, and consequently that there is much reason to doubt whether any member of the family did exist before the Eocene period. The existence of a Cretaceous Verruca is an apparent exception to the rule, as this genus has hitherto always been ranked amongst sessile cirripedes; but Verruca, as we now know, must be placed in a family by itself, quite distinct from the Balanidæ. Balanus is the oldest genus as yet known; it first appeared in Europe and North America, during the deposition of the eocene beds; and was at that time, as far as our information at present serves, represented by very few species. In South America, one species of Balanus abounds in individuals in the ancient Patagonian tertiary formation. I have seen, in the British Museum, specimens, said to have come form the eocene nummulitic beds near the mouth of the Indus, belonging to the second section of the genus. Generally, the extinct forms belong to the last section of this genus, which has the parietes not permeated by pores. During the miocene and pliocene ages, sessile cirripedes abounded. No extinct genus in this family has hitherto been discovered. It is singular, that though the Chthamalinæ approach much more closely than do the Balaninæ to the ancient Lepadidæ, of which so many species have been found fossil even in the older Secondary formations, yet that only one species of one genus of this sub-family has been hitherto found in any deposit; and that species is the still existing Pachylasma giganteum, in the modern beds of Sicily. During the epoch of the Glacial deposits in Scandinavia, Scotland, and Canada, the still existing species seem to have abounded; and they attained larger average dimen-

* Since the note to page 5 of that work was written, I have been informed that the so-called cretaceous Tubicinella maxima is not a Cirripede.

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sions than the same species now do on the shores of Great Britain, or even on the shores of the northern United States, where the average size seems larger than on this side of the Atlantic.

Under the genus Balanus, I have given my reasons for never naming species in this large and difficult genus, without examining the opercular valves: it has been owing to this, as it appears to me, proper want of caution, that there are so many nominal species. Thus it is made to appear in catalogues, that the tertiary seas abounded with species of Balanus to an extent now quite unparalleled in any quarter of the world. Bronn,* for instance, in his invaluable 'Index Palæontologicus,' gives the names of 35 Balani, found fossil in Europe, and I have not counted those found only in alluvial deposits, as they would certainly be the same as the still living species. Now I know only 11 recent Balani on the shores of all Europe, from the North Pole to lat. 30°; and of these I doubt whether B. balanoides and improvisus have been found fossil. In the Red Crag there is one extinct Balanus: in the Coralline Crag, which seems to have been very favorable to the existence of Cirripedes, there are six species of Balani, of which two are absolutely extinct, and one does not occur in any neighbouring sea: in the Eocene formations the species seem to have been rare, and I have seen only one, and that is an extinct form. Taking these several facts into consideration, and bearing in mind that Cirripedes usually range widely, I do not believe, if all the specimens of Balani hitherto found in the several tertiary formations, from the eocene to the glacial deposits, throughout Europe, were collected together, they would amount to 20 species. I have myself seen, in a recognisable state, only 12 fossil species, of which five are extinct, or not found in any neighbouring sea: I think it probable that three other recent species, viz. B. tulipiformis, perforatus, and amphitrite, may occur in the Mediterranean formations; and this would make 15 species. Therefore in the above estimate of 20 species, five are allowed for

* To save any other person, interested in fossil Cirripedia, going through the several works quoted by Bronn, I have given some remarks on his list of species, in an appendix at the end of the Balanidæ.

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species existing in European collections, but not hitherto seen by me; and this, I believe, is a very full allowance. Consequently, even on the supposition that the five species just admitted as possibly existing in cabinets, and that the other five extinct species, which I have seen and examined, have all been previously named by other authors, a supposition excessively improbable, even then there would be 15 superfluous names in Bronn.

The following short table shows how Cirripedes, including all three Families, were represented in Great Britain, throughout the several TERTIARY STAGES.

Name.
Living species, but found fossil in some tertiary deposit. Mammiliferous crag, and glacial deposits. Red crag. Coralline crag. Eocene.
Balanus 
tintinnabulum . *
. . * . . . .

calceolus . . . * . . . . *

spongicola . . * . . . . * . .

concavus . . . * . . . . * . .

porcatus . . . * * * . . . .

crenatus . . . * * * * . .

Hameri . . . * * . . . . . .

bisulcatus . . . . . . . * * . .

dolosus . . . . . * . . . . . .

inclusus . . . . . . . . . * . .

unguiformis . . . . . . . . . . . *
Acasta undulata . . .
. . . . . . * . .
Pyrgoma anglicum . . .
* . . . . * . .
Coronula barbara . . .
. . . . * . . . .
Verruca Strömia . . .
* * * . . . .
Scalpellum magnum . . . . . . . . * . .

quadratum . . . . . . . . . *
Pollicipes reflexus . . .
. . . . . . . . *
Total, 18, recent and extinct, found fossil in Great Britain in some tertiary deposit . .
9
5
6
9
3

As affording some standard of comparison by which to compare the number of fossil species, at any period, in relation to the number of species probably existing in the neighbouring seas during the same epoch, I may state that there are now living and propagating on the shores of Great Britain, 18 species belonging to the three Families

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included in the above table. I have not counted three species, in the genera Alcippe and Conchoderma, which, from the minuteness of their valves, it is hardly possible would be found fossil. On the other hand, I have included in the 18, five species of Lepas, which from floating and being oceanic, are more likely to be cast up on beaches, than to be imbedded in sedimentary deposits; so that 13 would, perhaps, be a safer number, as a standard of comparison. Now in the coralline crag, which seems to have been eminently favorable for the existence and subsequent preservation of Cirripedes, and which has been so well worked, only nine fossil species, as may be seen in the table, have been as yet discovered.

Sub-Family—BALANINÆ.

Shell with the rostrum having radii, but without alæ; lateral compartments all having alæ on one side and radii on the other side; parietes generally either porose, or longitudinally ribbed on their inner surfaces.

Mouth with the labrum notched in the middle, not swollen; palpi large, almost touching each other; mandibles generally with the lower teeth laterally double; third pair of cirri with their segments resembling those of the second pair.

First Section.

Scutum and tergum articulated together, or overlapping each other; each branchia composed of a single plicated fold.

Genera—Balanus; Acasta; Elminius; Tetraclita; Pyrgoma; Creusia; Chelonobia.

Second Section.††

Scutum and tergum (when both are present) not overlapping each other; basis membranous; parietes often deeply folded, with the outer lamina, towards the basis, generally

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imperfect; each branchia composed of two plicated folds; shell attached to living vertebrata.

Genera.—Coronula; Platylepas; Tubicinella; Xenobalanus.*

The Balanidæ may be divided into two sub-families; namely, the Balaninæ and Chthamalinæ and, in the former, the genera, as we see, may be very naturally grouped into two sections. The Balaninæ differ from the Chthamalinæ, as far as the shell is concerned, in the rostrum having radii but no alæ, all the lateral compartments having both radii and alæ; on the other hand, in the Chthamalinæ, the rostrum has alæ, and the rostro-lateral compartments radii on both sides, and therefore no alæ. These differences probably arise, as already explained, from the perfect confluence, in the Balaninæ, of the true rostrum with the rostro-lateral compartments. In Chelonobia, belonging to the Balaninæ, we see an intermediate state, with the fusion not quite effected; on the other hand, in one genus amongst the Chthamalinæ, namely, Pachylasma, we must look to the shell at a very early age, to find the rostrum with its alæ, distinct from the rostro-lateral compartments. In Tetraclita, Elminius, and Creusia, the carino-lateral compartments are aborted, or possibly confluent with the lateral compartments, making altogether only four: in Pyrgoma all the compartments are fused together and form a solid ring. The sub-genus Acasta is, in one sense, very natural, as it includes species most closely allied: in another sense it is far from natural, as some of the species can hardly be distinguished from those species of Balanus, which live attached to Gorgoniæ: I almost regret I did not merge the species of Acasta into Balanus. In the Balaninæ generally the parietes are either porose, or are furnished on their internal surfaces with regular ribs, representing the longitudinal parietal septa, which in other species form the tubes or pores; there are, however, many exceptions to this rule in several species of Balanus, in Acasta and Elminius,

* At the end of the volume a Synopsis is given, which will serve as a systematic index for the discovery of generic and specific names.

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all of which have the parietes of their shells internally quite smooth, or only irregularly roughened with points.

Looking to the animal's body, in the Balaninæ, the labrum is always notched in the middle, and is never swollen or bullate, for the outer and inner folds of membrane of which it is composed lie close together. The palpi are large, so that their tips almost touch each other. The mandibles, generally, have their lower main teeth laterally double. Of the cirri, the third pair invariably much more closely resembles, in its whole structure, and in its action, the second than the fourth pairs; and it is also generally separated by a small interval from the fourth pair.

I have already under the Family sufficiently entered on the relations of the Balaninæ to the Chthamalinæ, and of the genera, one to the other, so that I need not here add anything.

I can point out no difference in habits or geographical distribution between the Balaninæ and Chthamalinæ.

1. Genus—BALANUS, Auct.*

CONOPEA (pars generis). Say. Journal Nat. Sc. Philadelphia, vol. ii, part ii, 1822.

MESSULA (do.). Leach. Zoological Journal, vol. ii, 1825.

CHIRONA (do.). J. E. Gray. Philosoph. Transacts., 1835, p. 37.

Compartments six; basis calcareous or membranous; opercular valves sub-triangular.

Distribution.—Mundane: in the warmer seas.

General appearance.—The shape of the shell in the different species varies from depressed conical to cylindrical;

* The name Balanus was used, almost as at present, by Lister and Hill, before the introduction of the binomial system. Since that period the first two authors, as far as I know, who used this name, were Da Costa, in his 'Hist. Nat. Test. Brit.,' in 1778; and Bock, in the 'Naturforscher,' for the same year; Bock, however, applied it to a Chelonobia.

12                       

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the latter form being generally assumed when specimens are crowded together; but some species, as B. balanoides, crenatus, and lævis, seem more subject than others to be thus affected. The colour is either white, generally tinted by the yellowish or brownish epidermis, or any colour intermediate between bright pink and rich blue, purple being the prevailing tint. The persistence of the so-called epidermis is very different in different species, being even sometimes highly variable in the same species. The surface is either smooth or more commonly folded longitudinally, or sharply ribbed. The orifice differs in form from diamond-shape to trigonal; the carinal end, owing to the shape of the carina, being always sharper or narrower than the rostral end. The size of the orifice, in proportion to the shell, varies accordingly as the latter is more or less conical or cylindrical. The orifice is either entire or more or less deeply toothed, in proportion to the degree of obliquity of the summits of the radii and alæ. The radii almost always have smoother surfaces than the parietes. In some few species the radii are not developed, the sutures being marked only by fissure-like lines; in others they are very narrow, and in this case their upper margins are generally rounded and smooth, instead of being straight and jagged. The carino-lateral compartments are usually much narrower than the lateral compartments, occasionally in an extreme degree, as in B. allium. The shell is generally strong, sometimes to a wonderful degree; but the strength and thickness vary in the individuals of some of the species. By the action of hot caustic potash, the compartments in several species, such as B. Hameri and crenatus, separate on a touch; in others, they adhere so strongly as to prove that the sutures must be calcified together. In this genus we have the largest known sessile cirripede, viz., the B. psittacus, and on the other hand many small species; but it is very difficult, except in well-known species, to ascertain the average or even the maximum dimensions.

Scutum.—This valve is almost triangular, with the basitergal corner more or less rounded off. The prominent lines of growth are sometimes crossed by longitudinal striæ. Internally, the articular ridge projects to a very different

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degree in the different species; its lower end is sometimes (as in B. lævis, Pl. 4, fig. 2 c) produced downwards as a small, sharp, free style; there is always an articular furrow receiving the inflected margin of the tergum. There is always an impression left by the attachment of the adductor scutorum muscle; and often its lower side is bounded more or less closely by a sharp adductor ridge, running some way down the valve; this ridge is occasionally almost confluent, in its upper part, with the articular ridge, and in this case sometimes it forms, together with the inflected tergal margin, a large tubular cavity, running up, as in B. psittacus (Pl. 2, fig. 3 c), almost to the apex of the valve. Almost invariably there is a slight pit or depression for the lateral depressor muscle; sometimes within the depression there is a little ridge, as in B. perforatus and nubilus (Pl. 4, fig. 3 a, and Pl. 6, fig. 2 a); and in the case of B. vestitus, flosculus, and imperator (Pl. 8, figs. 3 a, 4 a), there are regular crests for this same purpose. The rostral depressor muscle is usually attached in a small pit formed by the folding over of the lower part of the occludent margin: in B. imperator (Pl. 8, fig. 4 a) there are regular crests for its attachment, and traces of them may be discovered in B. vestitus.

Tergum.—This valve is more nearly triangular than any other shape, with the spur more or less prominent. The apex generally projects a little above the level of the scutum; in some species it consists of a triangular and solid, in others (Pl. 2, fig. 3 b) of an almost cylindrical, extremely sharp, inwardly curved, and very prominent beak. This beak is generally purple; it is sometimes hollow, and occupied by a thread of corium. Its formation, and the apparent sliding up of the whole tergum, so as to project above the scutum, has been described under the family. From an account given to me by a person who kept B. porcatus alive, the beaks appear to be used, when the operculum is touched, as an organ of defence,—the animal striking with them. The tergal margin is more or less inflected; and the carinal margin is convex in different degrees, and, in some species, is added to by upturned zones of growth. The basal margin either forms a nearly straight line on opposite sides of the spur, or more commonly slopes towards it in various

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manners. The spur, or basal projection, is rarely placed in the middle of the basal margin, generally near, sometimes close to the basi-scutal angle; it varies much in length and breadth, and is sometimes even half the width of the valve. The surface of the valve is almost always more or less depressed, sometimes so much as to form a deepish furrow, the "longitudinal furrow," which extends from the apex to the extremity of the spur. When the furrow is deep, its sides, as the specimen grows old, almost always become folded inwards, so as to touch, and then the furrow becomes converted into a closed fissure: in this latter case the folded sides generally form a central crest on the spur. Internally, in the middle of the upper part of the valve, the articular ridge is more or less prominent, forming the carinal margin of the articular furrow, in which the articular ridge of the scutum is lodged; occasionally, however, this articular ridge can hardly be said to exist. In most species the tergal depressor muscle is attached to sharp crests on the basi-carinal corner of the valve, but these are almost obliterated in other species.

Compartments.—The external appearance of the shell has already been described. In the most typical species, the parietes consist of an outer and inner lamina, separated by strong longitudinal septa; these septa are denticulated on both sides at their bases, but only close to the inner lamina; in fact the inner lamina is apparently formed by the union, thickening, and production, of some of the denticuli. As it is not the innermost of the denticuli on the basal edges of the longitudinal septa, which thus become united into a solid layer, the longitudinal septa form slightly projecting, longitudinal ribs on the inner lamina. These internal ribs are longitudinally striated; in old specimens they often become obliterated, especially in the upper part of the shell. The parietal tubes or pores (occupied by threads of corium) are generally square and large; but in B. Ajax they are very small, and in B. glandula often extremely minute. In the upper part of the shell, and sometimes low down, they are generally crossed by thin, transverse, calcareous septa: in some species, as in B. perforatus, and in some varieties of B. amphitrite, the upper ends of the

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tubes are filled up solidly with shell. In some varieties of B. crenatus and of amphitrite, the longitudinal septa, near the outer lamina, divide, thus giving rise to a very imperfect row of outer short tubes. In B. vinaceus (Pl. 2, fig. 7 d) the inner lamina is cancellated instead of being solid, which is caused by the basal denticuli of the longitudinal septa being simply united together by their ends and crossed by transverse septa, instead of being consolidated into a mass. In several species, as in B. Hameri, the walls consist only of the outer lamina with longitudinal ribs, no inner lamina having been formed; the ribs here evidently answer to the longitudinal septa in the foregoing species. In B. flosculus and imperator the walls are solid, their basal margins being formed of irregular, elongated points, and little ridges (Pl. 8, fig. 4 c), which apparently prefigure the more regular longitudinal ribs or septa. In B. balanoides the walls are generally either nearly smooth and solid, or irregularly cancellated; in B. cariosus (Pl. 7, fig. 3 b) two or three rows of short irregular tubes are formed by unequally branching septa, almost as in the genus Tetraclita.

The Radii, in all the species, are constructed essentially on the same plan as the parietes; thus, in the typical forms, there is an outer and inner lamina, with septa, which, near the inner lamina, are furnished with denticuli on both sides; hence the radii are permeated by pores or tubes, like the parietes; but this holds good only in the first section of the genus, for, in the other species, the tubes are filled up quite solidly. The denticuli on the septa often occur only on one side, or disappear altogether; and, lastly, the septa themselves often appear merely like little teeth, or disappear altogether as in B. Hameri, or occur only near the bases of the radii, as in B. amaryllis. A slight furrow in the compartment, against which each radius abuts, is generally marked by the septa and their denticuli. In regard to the alæ, their lateral or sutural edges are either thin and smooth, or, more commonly, finely crenated or ribbed. The little transverse crenations are homologous with the septa in the radii and parietes. The edges of the alæ are usually received in a furrow. The diametric growth of the shell is

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effected by the growth of the radii and alæ, and chiefly by that of the former. The sutural and lateral edges of both radii and alæ are added to, either quite up to their summits, or only low down, and during the continued growth of the shell, lower and lower down; in accordance with this difference in growth, the summits of the radii and alæ become either very oblique, or they extend parallel to the basis, that is, from tip to tip of the adjoining compartments. When the radii and alæ are added to, as is most usual, above the level of the opercular membrane, and therefore above the sack, ribbons of corium run up the sutures from the sack, higher or lower, according to the height to which, in the different species, the edges of the radii and alæ continue to be added to. The obliquity of the summits of the radii and alæ varies, in some cases, in the same species. It often happens that when the summits of the radii are very oblique, the summits of the alæ are but little so; and the converse; both, however, are often either equally oblique, or both have square summits. The sheath extends either one third or more than half down the shell; its basal margin often (Pl. 25, fig. 1, K´) freely depends or overhangs the inner lamina of the walls.

Basis.—In typical species the basis is calcareous, and consists of an upper and lower lamina, separated by radiating septa, forming pores. In the same manner as the septa of the parietes sometimes, though rarely, become irregularly divided near the outer lamina, forming outer pores, so it is, but in a much more marked degree, with the basis. The basis in such cases becomes extremely thick, and consists of an upper, thin lamina, with the regular radiating septa and pores, and of an underlying, thick, cancellated mass, which seems wholly to result from the dividing and subdividing of the septa. The basal radiating pores, like the parietal pores, are closed at intervals by calcareous transverse septa. The basal points of the parietal septa enter the orifices of the basal pores, and the threads of corium pass into the latter, between the denticuli of the parietal septa. In some species, as in B. crenatus and Hameri, the basis is perfectly solid, the upper lamina being absent, just as in some species, the internal lamina of the

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parietes is absent. In B. flosculus the basis is calcareous, but consists of so excessively thin a film as hardly to be distinguished: it presents, moreover, as also is the case with B. imperator, a beaded structure. Again, in some few species, as in B. balanoides, the basis is simply membranous. When the basis is thin, it is always flat, and is closely moulded to the irregular surface of attachment; and in this case, when specimens are crowded together, their elongation is effected exclusively by the growth of the walls; but, when the basis is thick, it sometimes becomes, in crowded groups, deeply, but irregularly, cup-formed, or cylindrical, as in B. psittacus and perforatus. In B. allium, however, which inhabits massive corals, the basis is as regularly concave or cup-formed as in the genus Pyrgoma: in B. calceolus and its allies, and in some varieties of the fossil B. inclusus, the basis is boat-formed, with its lower surface deeply grooved longitudinally from clasping the stem of the Gorgonia or other zoophyte, to which it was attached. In certain varieties of B. lævis it is very remarkable that the deeply cup-formed basis becomes, owing apparently to the whole shell having grown too deep for the animal, half-filled up with irregular, calcareous, transverse plates (Pl. 4, fig. 2 a), resting one upon the other by irregular points or pillars. The cementing apparatus has been sufficiently described under the Family.

Mouth.—The labrum is always notched; sometimes it has no teeth, but generally there are three on each side; in B. balanoides there are five or six on each side; and in B. improvisus and eburneus there is a whole row of teeth (Pl. 26, fig. 2, ), graduated in size, on each side of the notch. The palpi are large, with their apices nearly touching, and furnished with long spines. The mandibles have, as it appears, normally, five teeth, but the two lower teeth are always small and often rudimentary, and almost confluent with the inferior, sometimes spinose angle. The maxillæ have either a simple edge, or a notch under the pair of large upper spines, or the lower part forms (Pl. 26, fig. 7) a step-formed projection: there are generally two lower spines, placed singly or not in pairs, larger than the

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others, with the exception of the uppermost pair. The outer maxillæ are, on their inner faces, obscurely divided into two lobes.

Cirri.—The rami of the first pair are unequal, the shorter one sometimes not being more than half the length of the other ramus: the segments of the shorter ramus are broad, and are, together with the lower segments of the longer ramus, thickly clothed with spines; in some species, as in B. perforatus, the anterior surfaces of the segments, more especially of the shorter ramus, and of both rami of the second pair are produced (Pl. 29, fig. 4), so as sometimes to form very remarkable projections. The segments of the second and third pairs are always thickly clothed with spines, as also are their pedicels. The third pair is rather longer than the second; but in B. vestitus and imperator it is much longer, and is otherwise somewhat different. The dorsal and basal margin of the pedicel of the third pair, in some of the species, as in B. tintinnabulum, is produced backwards on the thorax, and forms a membranous plate fringed with fine spines. The three posterior and longer pairs of cirri have from three to rarely eight or ten pairs of long spines on each segment, with generally one or two minute spines in the middle between each pair: their pedicels have a regular double row of spines.

The penis is long and hairy: in most of the species there is, at its dorsal basis, a small, sharp, flattened, imperforate projection; first observed by Poli: but this is sometimes absent, as in B. crenatus, though present in the closely allied B. balanoides; and its presence is variable in B. tintinnabulum. All the species have large plicated branchiæ. The base of the sack in several species is furnished with inwardly projecting filamentary appendages. In B. perforatus, crenatus, and improvisus, and I believe in other species, the upper part of the stomach is furnished with a circle of branching cæca.

On the variation of the species; their arrangement and affinities; value of the characters used; changes during growth.—Owing to the great variation in external characters, to which almost all the species are subject, and likewise to

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the genus being a very natural one, that is, to the species following each other in close and natural order, it is not easy to exaggerate the difficulty of identifying the species, except by a deliberate examination of the internal and external structure of each individual specimen. Every one who has collected sessile cirripedes must have perceived to what an extent their shape depends on their position and grouping. The surface of attachment has a great effect on that of the shell; for as the walls are added to at their bases, every portion has at one time been in close contact with the supporting surface; thus I have seen a strongly-ribbed species (B. porcatus) and a nearly smooth species (B. crenatus) closely resembling each other, and both having a peculiar appearance, owing to their having been attached to a pecten. Dr. Gray has pointed out to me specimens of B. patellaris, curiously pitted like the wood to which they had adhered; and numberless other instances might be added. Quite independently of the effect produced by the surface of attachment, the degree to which the longitudinal folds and ribs are developed on the parietes, is variable in most of the species, as in B. tintinnabulum, vestitus, and even in B. porcatus; the presence or entire absence of these ribs often surprisingly alters the whole aspect of the shell. The persistence of the so-called epidermis is in some degree variable; and in B. lævis we have groups of specimens absolutely naked, and others uniformly clothed with a brown membrane. Again, some species in certain localities are all subject to the disintegration of the entire outer lamina of the walls; and in such cases (as with B. perforatus) there is not the smallest resemblance between the corroded and perfect specimens. The size of the orifice, and consequently of the operculum, compared with the shell itself, varies accordingly as the shell is more or less conical or cylindrical; in the latter case, the summits of the radii are generally more oblique and the aperture consequently more deeply toothed than in the more conical varieties. Size is a serviceable character in some cases, but very many specimens are required to ascertain the average or maximum size of each species, for there is no method of distinguishing a half-grown from a

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full-grown specimen; and I believe, as long as the individual lives, so long does it go on moulting and growing. Colour is of very considerable service; though the precise tint varies greatly in almost every species; and what is a far more serious evil, the majority of the species have their white or nearly white varieties, the latter sometimes as numerous as the coloured ones: in B. perforatus, lævis, flosculus, amphitrite, and in several other species, the common white varieties are eminently deceptive.

Besides the slight variation in the obliquity of the summits of the radii and alæ, dependent on the more or less cylindrical form of the shell, in some species, as in B. tintinnabulum, amphitrite, improvisus, trigonus, and porcatus, their obliquity also varies occasionally from unknown causes, and thus greatly affects the general appearance of the shell. In some few species, as in B. perforatus, the radii are often either not at all developed, or are of very variable width; in others, when the shell has become cylindrical, or when very old, the radii cease to grow, and from the disintegration of the whole upper part of the shell, with the continued growth of the lower part, the radii at last come to exist as mere fissures: I have seen instances of this in B. psittacus, nigrescens, and porcatus. Nevertheless, the obliquity of the upper margin, and the breadth of the radii are useful characters; and still more useful is the fact whether the upper margins are smooth and arched, or straight and jagged. The fact of the terga being more or less beaked is useful: as is, likewise, the presence of striæ, or furrows, or rows of pits, radiating from the apices of the scuta; but to ascertain the presence of these marks, it is almost invariably necessary to take out the scuta, clean, and examine them with a lens; these ridges and furrows, moreover, in some species, as is strikingly the case with B. tintinnabulum, and in less degree with B. trigonus, lævis, and concavus, appear and disappear, and vary without any apparent cause.

Now if we reflect that form, size, state and nature of the surface, presence of epidermis, relative size of the orifice, presence of longitudinal ribs, tint, and often the existence of any colour, are all highly variable in most of the species; and that the obliquity of the summits of the

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radii, and the presence of longitudinal striæ on the scuta, are variable in several species; we shall perceive how difficult it must ever be to distinguish the species from external characters. As some evidence of this, I may mention that, after having described nearly 40 species, and when my eye was naturally able to appreciate small differences, I began carefully to examine varieties of B. tintinnabulum, amphitrite, improvisus, porcatus, vestitus, &c., without even a suspicion that they belonged to these species, at that time thoroughly well known to me; yet in the cases here referred to, there could be no doubt, when a perfect series was examined, that the specimens were only varieties. From this cause the labour of naming a collection is great. Let no one attempt to identify the species of this genus, without being prepared to disarticulate, clean, and carefully examine with a microscope the basis and parietes, and both the under and upper surfaces of the opercular valves; for I feel convinced, that he will otherwise throw away much labour. Moreover, in many cases, it is almost necessary, on account of the variability of the characters, to possess several specimens. From these facts, I have not hesitated to form my sections on characters which require close examination, though I would gladly have seized on external characters, could I have found such even moderately constant.

The least varying, and therefore most important characters, must be taken from the internal structure of the parietes, radii, and basis: not that these characters are absolutely invariable; thus the porosity of the parietes is slightly variable in B. glandula, and highly variable in the fossil B. unguiformis; it is also highly variable in B. balanoides, but under a systematic point of view this is unimportant, as the section including this latter species is well defined by the membranous basis. The porosity of the basis is in some degree variable in B. nubilus, improvisus, and patellaris; and in B. flosculus we see signs of a passage from a calcareous to a membranous basis. Characters derived from the general shape, and from the ridges and depressions on the under side of the scuta and terga, especially of the scuta, are highly serviceable. The terga, indeed, in many species, as in B. amphitrite, vary con-

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siderably, and are affected by the general shape of the shell. Unfortunately the differences are not very great between the scuta of the different species. The cause of the opercular valves offering more useful characters, as far as outline is concerned, than do the walls of the shell, is no doubt due to their being almost independent of any influence from the nature of the surface of attachment. Even the ridges and depressions on the under side of the scuta, which are in direct connection with the muscles and soft parts of the animal, vary to a certain extent: thus the length and prominence of the adductor ridge is decidedly variable in B. concavus and tintinnabulum, and in a less degree in B. lævis; the size and form of the little cavity for the lateral depressor muscle varies in many species; so does the exact shape and degree of prominence of the articular ridge. There is one character in the terga, which at first would be thought very useful, namely, whether an open longitudinal furrow, or a closed fissure runs down the valve from the apex to the spur; but it is found that the furrow almost always gradually closes up during growth; and as a consequence of this, the width of the spur compared to that of the whole valve, as well as its distance from the basi-scutal angle, and the form of its basal extremity, all vary in some degree. The length of the spur sometimes varies considerably, as in B. concavus and amphitrite. The parts of the mouth are only occasionally serviceable; for the teeth on the labrum, and the state of the lower teeth on the mandibles, and the presence of a step-formed projection at the lower angle of the maxillæ, are all often variable. The relative lengths of the two rami of the first pair of cirri, the degree of protuberance of the segments, and the number of pairs of spines on the segments of the posterior pairs of cirri, are sometimes useful; but the relative lengths of the cirri, and more especially the numbers of pairs of spines on the posterior cirri, are apt to vary. Finally, I must express my deliberate opinion, that every part and organ, internal and external, in Cirripedes, is liable to some amount of variation in some of the species.

I must now point out the principal changes which super-

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vene during growth, and which cannot properly be called variations. In the first place, I think, it is scarcely possible to recognise a species when under the 1/10th of an inch in diameter. In some cases, as in var. d'Orbignii of B. tintinnabulum, the shell is invariably coloured when old, but quite white when very young. Generally the tints become very much darker with age. Some species, which usually or invariably have, when mature, longitudinally folded walls, as B. flosculus and balanoides, are perfectly smooth in youth. The walls in B. eburneus, when young, have white, hyaline, longitudinal lines, and are naked; whereas, with advancing age, these lines disappear, and the subsequently formed shell becomes covered with membrane. The summits of the radii are apt to be oblique in the young of B. Capensis, psittacus, and tintinnabulum, whereas they are generally quite square in old specimens. In B. eburneus, cariosus, and in a lesser degree in B. psittacus, the scuta become longitudinally striated only with age. On the other hand, in very young specimens of B. tintinnabulum, the scuta sometimes are deeply impressed by little pits placed in rows. I have already alluded to the longitudinal furrow on the tergum so entirely changing its character, owing to the edges becoming, during growth, folded inwards; this likewise causes a decrease in the proportional breadth of the spur. In old specimens of B. flosculus, var. sordidus, the whole tergum is much more elongated than in young specimens. The basal margin of the sheath is hollow beneath in the young of B. cariosus and of some other species, but in the old it is continuous with the inner surface of the walls. The inner lamina of the parietes generally loses, to a certain extent, its longitudinally ribbed character in old age. The basis is solid, instead of being porose, in very young specimens of B. improvisus. In all the species, the carino-lateral compartments, in early age, are very narrow in proportion to the width of the lateral compartments; and in all, at this early period, the operculum is large in proportion to the whole shell. The number of spines on the edge of the maxillæ, the number of segments in all the cirri, and the number of spines on each segment, are few in early youth, and go on increasing with

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each successive exuviation: the pedicels of the cirri are long in proportion to the rami at this same early age.*

Notwithstanding the difficulties now enumerated, I hope that, owing to having examined a vast number of specimens of the most varying species, I have not fallen into very many errors. I have endeavoured to err on the side of making too few instead of too many species. In those cases, however, in which I have seen only a few specimens, I have been sometimes compelled to decide without sufficient evidence.

I would gladly have divided this genus, already including 45 species, into smaller genera; but so far from being enabled to do so, I have been compelled to form my Sections (immediately to be given) on characters not absolutely invariable, and far from obvious. I was particularly anxious to separate the elongated species with a boat-formed basis, which are attached to Gorgoniæ, and which form the genus Conopea of Say, but I was unable to effect their separation even as a sub-genus; for B. navicula and cymbiformis graduate in the most insensible manner through B. galeatus (the type of Say's genus) and B. calceolus into B. stultus, and this into B. Ajax; yet this latter species has even been described as a mere variety of the typical B. tintinnabulum! Indeed, so insensible is this graduation, that the first and second sections of the genus are hardly distinct. I fully

* In some specimens of Balanus perforatus I made the following enumeration of the number of segments in the cirri:—


Basal diameter of shell 1/20th of an inch. Basal diameter of shell 1/5th of an inch. Medium sized specimen about 3/4ths of an inch in basal diameter.
First cirrus shorter ramus ? 11 17
Second cirrus 4 or 5 9 13
Sixth cirrus 9 or 10 19 31, in another 36

In the specimen 1/5th of an inch in basal diameter, each segment of the posterior cirri carried five pairs of spines; whereas, in full-grown specimens, there are six or seven pairs. In the 1/20th of an inch specimen, on the inner maxillæ; there were no spines between the upper large and the lower large pair of spines; whereas, in the 1/5th of an inch specimen, there were five intermediate spines, and in larger specimens nine or ten spines.

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admit, that if B. stultus and Ajax had never existed, B. calceolus and its three allies might have formed as natural a little group, though difficult to be characterised, as does the sub-genus Acasta; or perhaps this group and Acasta might have been combined together. These same species, viz., B. calceolus and its allies, are intimately allied to B. terebratus and inclusus, which are contained in the last section (F) of the genus; and this shows that Dr. Gray's proposed genus Chirona, including the species with non-porose parietes in sections (E) and (F), could hardly have been instituted, even if the porosity of the parietes had not been variable in B. unguiformis, balanoides, and glandula. My fourth section (D), founded on the basis not being porose, is perhaps the weakest of the divisions, as may be seen in the list of exceptions appended to the sectional headings.

The arrangement of the species is, I think, as natural as a linear one could be made: every one knows how irregularly and in how many directions the lines of affinity in every natural genus branch out. Some few species stand rather isolated, as B. declivis; and B. allium, cepa, and quadrivittatus in a little group by themselves. I have already shown how the species in the first and second sections (A and B) blend into each other; and that the blending species are likewise allied to some in the last section (F); furthermore, I shall have occasion to show that these same species can hardly be separated naturally from the sub-genus Acasta. The first section, moreover, passes into the third (C) by B. tulipiformis; and the third into the fourth (D) by B. improvisus, nubilus, corrugatus, and patellaris: the fifth and sixth (E and F) sections are closely connected together by B. cariosus and flosculus; and these two sections blend into the fourth (D) through B. unguiformis and balanoides, and lastly, into the third (C) section by B. dolosus and improvisus.

The genus, as we have just seen, is hardly separated from the sub-genus Acasta; by B. allium it tends to pass through the sub-genus Creusia into Pyrgoma; and by B. imperator and flosculus it graduates into Elminius and Tetraclita.

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Geographical Distribution.—This, which is much the largest genus of sessile cirripedes, has its species scattered over the whole world, from the arctic regions, in lat. 74° 48´, where we have B. crenatus and porcatus, throughout the tropical seas, to Cape Horn, where B. flosculus adheres to the coast-rocks. Many of the species have individually very wide ranges; thus B. tintinnabulum and amphitrite are found throughout the warmer seas; but the wide distribution of these species may be partly due to their frequent adhesion to ships' bottoms: B. crenatus ranges from the frozen seas, in lat. 74° 48´ north, to the West Indies and Cape of Good Hope—a wonderful endurance of the most opposite climates. Balanus improvisus, again, extends from Europe to Nova Scotia, thence southward to Patagonia, and up the western coast of S. America, someway north of the Equator. Most of the species have considerable ranges; thus of the six species found on the eastern shores of northern America, five of them occur in Great Britain. Of the thirty-six species of which the habitats are known, exactly one third, or twelve, inhabit both the torrid and temperate zones, these being divided by the isocryme of 68°; nine are found exclusively in the torrid, and fifteen exclusively in the temperate zones. Within the warmer latitudes, and especially in the southern hemisphere, Tetraclita and Elminius to a certain extent supplant Balanus. In depth, the species range from the upper limits of the tidal zone to even fifty fathoms. Balanus improvisus and eburneus are able to survive in brackish water. The different species are attached to various surfaces—rocks, shells, timber, floating objects, sea-weed, lamelliform corals, Milleporæ, Gorgoniæ, and even to sponges. Mr. G. B. Sowerby has remarked* that in the species from the southern hemisphere it is the basis, and in the species from the northern hemisphere it is the parietes, which are elongated, when the individuals, from being crowded together, become cylindrical; but this is erroneous; B. perforatus, in the northern hemisphere, sometimes has an elongated basis; but no doubt the basis of our commonest species, as B. balanoides, crenatus, and porcatus,

* Darwin's 'Geology of S. America.' p, 264.

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from being either membranous or thin, does not become cup-shaped; whereas this structure is conspicuous in B. psittacus and lævis, the two commonest species in southern South America.

Fossil Species.—Having already given, under the Family, some account of the geological history of sessile cirripedes, short as it is, I here only allude to the subject in order to state my conviction that species cannot be satisfactorily distinguished in a fossil state, and rarely in a recent state, without an examination of the opercular valves. Nothing, indeed, could have been easier than to have affixed names to many groups of specimens, having different aspects, but to feel sure that these were really distinct species requires better evidence than can be afforded by the shell, without the operculum. No doubt, in some of the smaller sections of the genus—for instance, in that characterised by a membranous basis—it would have been possible to have distinguished some or several fossil species; but such have not as yet been found. When the specimens are much fossilised, it is, indeed, difficult to make out the primary points of structure—namely, whether the parietes, radii, and basis are porose: to do this it is sometimes necessary to rub down, polish, and carefully examine, a transverse section of a piece of the shell.

Sections of the Genus.

[A]

Parietes, and basis, and radii permeated by pores.

[B]

Parietes and basis sometimes permeated by pores, sometimes not; radii not permeated by pores; shell elongated in its rostro-carinal axis; basis boat-shaped, attached to Gorgoniæ and Milleporæ.

[C]

Parietes and basis permeated by pores; radii not permeated by pores.

13                          

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[D]

Parietes permeated by pores. Basis and radii not permeated by pores.

[E]

Basis membranous.

[F]

Parietes and radii not permeated by pores. Basis sometimes permeated by pores, sometimes not, sometimes excessively thin and hardly distinguishable.*

————

Section A.

1. BALANUS TINTINNABULUM. Pl. 1, fig. a-l: Pl. 2, fig. 1 a-1 o.

LEPAS TINTINNABULUM. Linn. Syst. Naturæ, 1767.

— — Ellis. Phil. Transact., vol. 50, 1758, Tab. 34, figs. 8 and 9.

————————————————————————————————————————————

* The following species might, owing to variation, or to the obscurity of their structure, without care, be classed in the wrong sections:—In A, Balanus Ajax, from living attached to Milleporæ, is sometimes elongated in its rostro-carinal axis, and from having its radii only finely porose, it might be classed in B: on the other hand, Bal. stultus is sometimes but little elongated, and the basis hardly boat-formed, and hence might be classed in A. The distinction between all the species in (B) and the sub-genus Acasta is artificial.

In sections C and D, I have seen one specimen of B. spongicola with a solid basis, and very young specimens of B. improvisus are thus characterised, and therefore these species are liable to be placed in the wrong section, D: Bal. nubilus, also, has part of its base non-porose, and therefore likewise might be placed in D: on the other hand, the circumference of the basis in B. patellaris is often porose, and hence this species, which belongs to D, might be placed in C.

In Bal. glandula, in D, the parietes of the compartments, without several were examined, might be thought to be solid, and therefore this species might be wrongly placed in F; on the other hand, the fossil B. unguiformis, in F, often has porose parietes, and such specimens would naturally be placed in D. Lastly, without care, B. flosculus might be thought to have a membranous basis, and so get placed in E.

The genus Pachylasma, without an examination of the animal's body, might easily get misplaced in the wrong genus, amongst the species in the last section (F) of Balanus, yet there can be no doubt that Pachylasma belongs to the Chthamalinæ.

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LEPAS TINTINNABULUM. Chemnitz. Neues. Syst. Conch., 8 B. (1785), Tab. 97, figs. 828-831.

BALANUS TULIPA. Bruguiere. Encyclop. Meth., 1789; sed non B. tulipa alba, in Chemnitz; necnon B. tulipa, O. F. Müller, Zoolog. Dan.; nec non B. tulipa, Poli, Test. ut. Siciliæ.

— — G. B. Sowerby. Genera of Recent and Fossil Shells, Tab. Genus Balanus.

LEPAS CRISPATA (var.) Schröter. Einleitung Conch. vol. iii, Tab. 9, fig. 21.

— SPINOSA (var.) Gmelin. Linn. Syst. Nat.

— TINTINNABULUM, SPINOSA, CRISPATA ET PORCATA. W. Wood. General Conchology, 1815, Pl. 6, figs. 1, 2. Pl. 7, figs. 4, 5. Pl. 8, figs. 1-5.

BALANUS TINTINNABULUM. Chenu. Illust. Conch.*

— D'ORBIGNII. (var.) Chenu. Illust. Conch., Tab. 6, fig. 10, sed non Tab. 4, fig. 13.

— CRASSUS (Foss.) Sowerby (!). Min. Conch., 1818. Tab. 84.

Shell varying from pink to blackish purple, often striped and ribbed longitudinally: orifice generally entire, sometimes toothed. Scutum with the articular ridge broad and reflexed. Tergum with the basal margin generally forming a straight line on opposite sides of the spur.

Var. (1) communis (Pl. 1, figs. a, b, f supra: Pl. 2, figs. 1 a, 1 c, 1 d, 1 e, 1 i, 1 k): conical or tubulo-conical; smooth or moderately ribbed longitudinally; colours varying from purplish-pink to blackish-purple; often in obscure longitudinal stripes; orifice of shell rounded-trigonal.

Var. (2) vesiculosus (young) (Pl. 2, fig. 1 h): exterior surface of the scuta impressed with small square holes, arranged in two or more rows, radiating from the apex of the valve.

Var. (3) validus (Pl. 1, figs. c, f infra): globulo-convex; coarsely ribbed, ribs flexuous; either smooth or rugged; pale chocolate purple or pink; shell extremely strong; orifice almost circular.

Var. (4) zebra (Pl. 1, fig. g): conical; rich chocolate purple with broad snow-white ribs; sheath bright chesnut colour; summits of alæ oblique; orifice almost circular.

Var. (5) crispatus (Schröter) (Pl. 1, fig. h): pale blueish or pinkish-purple, with irregular rough projections, or with short, sharp, needle-

————————————————————————————————————————————

* Chenu gives several admirable figures of this species; but he confounds some forms certainly distinct under this name, for instance the B. tulipiformis of this work.

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like points; scuta with their exterior surface either plain, or with radiating lines formed of hood-like projecting points.

Var. (6) spinosus (Gmelin): (Pl. 1, fig. i): globulo-conical or cylindrical; shell rather thin, with long, upcurved, nearly cylindrical, very sharp points; colours very pale; attached to other specimens, and to Lepas anatifera.

Var. (7) coccopoma (Pl. 1, fig. d; Pl. 2, fig. 1 f, 1 l, 1 o): globulo-conical; orifice small, rounded; walls generally smooth, thick; intense rose-colour, sometimes most faintly striped longitudinally with varying shades of pink; radii tinged with purple; scutum sometimes as in var. communis, sometimes with its basi-tergal corner much cut off, with the adductor ridge prominent, the pit for the depressor muscle deep, and the articular ridge broad and hooked; tergum sometimes as in var. communis, sometimes with a broader spur, placed nearer to the basi-scutal corner of the valve.

Var. (8) concinnus (Pl. 1, fig. e: Pl. 2, fig. 1 g): globulo-conical; walls finely ribbed; dull purple, tinged and freckled with white; scutum, with a broad, hooked, articular ridge, with an extremely sharp plate-like adductor ridge, and with a cavity, bordered by a plate, for the rostral depressor muscle; tergum as in var. 4.

Var. (9) intermedius: radii with their summits slightly oblique; parietes pale blueish-purple, with narrow dark purplish-blue longitudinal lines; sheath with the internal surface of the rostrum and lateral compartments much darker colored than the internal surface of the carina and carino-lateral compartments; scuta and terga as in var. communis.

Var. (10) occator (Pl. 1, fig. k: Pl. 2, 1 b): radii with their summits slightly oblique; parietes smooth, or ribbed, or spinose; very pale blueish-purple, with narrow darker longitudinal lines; sheath with the internal surface of the rostrum and lateral compartments dull blue, whilst the corresponding parts of the carina and carino-lateral compartments are white; scuta with small, sharp, hood-formed points, arranged in straight radiating lines; terga with the spur placed at either its own width, or less than its own width, from the basi-scutal angle.

Var. (11) d'Orbignii (Chenu) (Pl. 1, fig. l: Pl. 2, 1 m, 1 n): radii with their summits oblique, and the orifice of the shell rather deeply toothed; shell conical or tubulo-conical, smooth, or rugged; colour dull purplish-lilac, with the tips of the parietes and a band along one side of the radii quite white; sheath rather darker at the rostral than at the carinal end; scuta as in var. 1; terga as in var. occator.

Habitat.—West coast of Africa, on mytili: Madeira, on rocks: West Indies: Cape of Good Hope, on a patella and on kelp: mouth of the Indus: East Indian Archipelago: Sydney, Australia, attached to Lepas anserifera, adhering to a floating cane: Peru; Galapagos Islands; West Mexico; California. Extremely common on ships'-bottoms arriving from West Africa, India, and China, often associated with B. amphitrite.

Fossil.—Red Crag, England; Mus S. Wood and J. de C. Sowerby.—Touraine (?); Mus. Lyell.

General Remarks.—This, the first species of Balanus, is, perhaps with the exception of B. amphitrite, the most difficult and variable in

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the genus. There are some other species which vary quite as much in external appearance; for instance, B. perforatus; but B. tintinnabulum also varies in far more important points, as in the proportions and structure of the opercular valves. The difficulty in determining whether or not the differences are specific, is wonderfully increased by whole groups of individuals varying in exactly the same manner. I have seen three most distinct varieties taken from the bottom of the same vessel, so that I did not at first entertain the least doubt that they were three distinct species. I may mention, as showing the vacillations which I have experienced on this subject, that beginning with the impression, that the above three varieties were really distinct species, after going over the several immense collections of specimens placed at my disposal, I came to the conclusion that the above three, and several other forms presently to be described, were only varieties; yet after an interval of some months, having to look at some of these specimens again, I could not but think that I had come to a false conclusion, and so went into all the details again, and satisfied myself that I had followed a right course; after another interval, I had to repeat the same process, and even now I can never look at a group of the beautifully coloured shells with their small rounded orifices of var. coccopoma attached to the Avicula margaritifera, or again at var. d'Orbignii, with its toothed orifice and white tips to the compartments, without thinking that they must be specifically distinct from the dull-coloured specimens with large entire orifices so common on ships' bottoms; yet I can produce a full series of intermediate forms, and I can further show, in each variety, that the several points of difference by which each is characterised, are variable. I may be permitted to add, in order to show that it has not been from indolence that I have combined so many forms, that I had named and already written out full descriptions of most of the varieties, before determining to sacrifice them.

Seeing that B. tintinnabulum and amphitrite are the two most variable species in the genus, more especially in the important characters derived from the opercular valves, and knowing that these species are attached so very frequently to ships' bottoms, one is led to suspect that their extreme tendency to vary may be due to their being exposed to varying and peculiar conditions, whilst transported to new and distant localities. It is even just possible, as may be inferred from the facts given in the Introduction (p. 102) in regard to certain monstrous specimens of Bal. balanoides having been apparently impregnated by adjoining individuals, that the varieties may interbreed, and so produce numerous intermediate forms. Whether or not this could take place, I am inclined to look at these two species, as in an almost analogous condition with our domestic animals, which give rise to such infinitely numerous varieties. It appears to me probable, that several of the varieties keep true to their peculiarities, as long as they continue to breed in the same locality; but that when their larvæ become attached to ships' bottoms, and are thus transported and exposed to new conditions, they give rise to new and ever-varying varieties. I will first give a full description of the more common forms of B. tintinnabulum, which undoubtedly belong to the same species,

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only alluding to the less frequent points of difference, and then separately describe the more marked varieties.

General Appearance.—Shape of shell generally tubulo-conical, or conical, or globulo-conical, rarely depressed. Orifice either large and rounded-trigonal, or small and oval, either entire or less frequently toothed. Surface quite smooth, or longitudinally ribbed; ribs of variable strength, not unfrequently flexuous or branching, sometimes roughened with blunt or sharp projecting, irregular points, or more rarely with almost cylindrical, upturned, long spines; the simple longitudinal ribs are generally most strongly marked in young specimens. Colour, generally varying from pink, to pink tinged with purple, to dark, inky purple, more or less striped, longitudinally, with white or pale tints; rarely the shell is of the brightest rose-colour, either uniform or longitudinally striped; sometimes it is pale purplish, or dark blue; and sometimes dark chocolate-purple: the ribs, when present, are generally more or less white, sometimes snow-white. That there is much variation in colour, and in the prominence of the longitudinal ribs, is quite certain, as the two sides of the same individual sometimes differ greatly in these respects. The radii are generally rather darker coloured than the parietes, but sometimes they are lighter, even in the darkest tinged specimens. The surfaces of the radii are occasionally finely plaited in lines parallel to the basis. In some infrequent varieties the radii have oblique summits, making the orifice of the shell to be toothed. The sheath is generally feebly coloured, but sometimes bright chesnut-brown, and sometimes blueish. The strength of the shell varies considerably; some of the globulo-conical varieties are extremely massive. Size; basal diameter of largest specimen very nearly three inches; height of the highest specimen three inches.

Young specimens are apt to have a peculiar aspect; for their shell is often strongly ribbed longitudinally, and the summits of their radii are sometimes oblique. Their scuta are sometimes deeply pitted in radiating lines. Their colours are generally pale. I have seen specimens attached to kelp from the Cape of Good Hope, with their parietes white and ribbed, and their radii mottled with pinkish-purple; I have seen other young specimens from the Galapagos Archipelago, of a uniform greyish-blue.

The Scuta generally have their lines of growth moderately prominent; occasionally they are longitudinally striated, with the lines of growth flexuous and upturned at intervals into small, sharp, hood-like projections, which are symmetrically arranged in straight lines radiating from the apex of the valve; I have seen this structure in some specimens of var. crispatus and in var. occator (Pl. 2, fig. 1 b); and I have noticed an intermediate state in var. communis. The degree to which the basi-tergal corner of the valve is rounded off varies much even in var. communis (Pl. 2, fig. 1 a, 1 d, 1 e). The articular ridge (1 c, 1 e) is broad and much reflexed; and often, but not always, distinctly hooked (1 f ). The adductor ridge is confluent with the articular ridge, and runs straight down the valve, bounding the cavity for the depressor muscle; generally the adductor ridge is blunt, and so little prominent as barely to deserve notice; but I have seen it sharp and prominent in

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one specimen of var. communis, and it is generally prominent in var. coccopoma (1 f ), and most remarkably so in var. concinnus (1 g). The cavity for the lateral depressor muscle is generally very slight; but in the two vars. just mentioned, and sometimes in var. communis, it is deep. In var. concinnus (1 g) there is a remarkable plate developed for the attachment of the rostral depressor muscle. The scuta are coloured either dull-purple or reddish, or striped longitudinally white and blue. The surface is sometimes externally depressed in the line of the adductor ridge; and in young specimens there is sometimes, along this line, a chain of pits (1 h), as in full-grown specimens of B. trigonus and lævis.

The Tergum (Pl. 2, figs. 1 i to 1 o) is broad, with a generally closed longitudinal furrow; this furrow is open in young specimens, and it is often, but not always, open in rather large specimens of var. occator; it is always open in var. d'Orbignii (Pl. 2, fig. 1 m), and sometimes in var. concinnus. Apex barely beaked, except in var. spinosus, in which it is sensibly produced. Spur placed either very nearly in the middle of the basal margin, or when least medial, it stands at above its own width from the basi-scutal angle; yet in some specimens of var. occator the spur is less than its own width from this angle. The basal margin (1 i), on opposite sides of the spur, either forms a nearly straight line, or the scutal portion descends lower than the carinal portion, and curves very regularly towards the spur; this is the case in var. d'Orbignii (1 n), and in some specimens of var. occator. The carinal half of the basal margin generally forms an angle with the spur of only a little above a rectangle. The spur varies a little in length and breadth, but never exceeds one fourth of the greatest breadth of the valve. The scutal margin is broadly inflected, the inflected portion forming either a right angle, or somewhat less than a right angle, with the exterior surface of the valve. Internally the articular ridge is prominent, and is either considerably or slightly curved; it extends down either about half, or three fourths, of the length of the valve. The spur is produced for a considerable distance up the internal surface of the valve as a prominence. The crests for the tergal depressor muscle are very feeble. In one specimen, in which both the shell and operculum had undergone much disintegration, the scuta and terga were calcified together.

Compartments: their exterior appearance has been already described. The parietal tubes are not large; they are generally crossed by transverse septa in their uppermost part; but they are sometimes almost solidly filled up by dark shelly layers. The internal surface of the parietes is more or less plainly ribbed; in old specimens, however, it generally becomes smooth. The radii have their septa denticulated on both sides; and they are porose, that is, the interspaces between the septa are not filled up solidly. The radii generally extend from tip to tip of the adjoining compartments, that is, their summits are parallel to the basis; but in three not common varieties, viz., vars. intermedius, occator, and d'Orbignii (the former of which at least must, without the smallest doubt, be ranked as a mere variety), their summits are oblique. I have occasionally met with specimens of var. communis with oblique

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radii; and this is not very infrequent in young shells. Exteriorly the radii are generally smooth, but sometimes finely ribbed horizontally, owing to the projection of the septa. The alæ have their sutural edges smooth; their summits are usually parallel to the basis, but they are often much broken; in var. zebra, however, in every specimen which I examined, the summits were oblique. The sheath varies much in colour: in var. occator, and in a less degree in var. intermedius and var. d'Orbignii, the portion lining the rostrum and lateral compartments is much darker than the other parts of the sheath. The Basis generally has a thick, underlying, cancellated layer. Sometimes the basis (Pl. 1, fig. b) is irregularly cup-formed.

Mouth: labrum with four or six minute teeth: mandibles with five graduated teeth; inferior point more or less spinose. Maxillæ, either with or without a small notch, beneath the upper pair of spines; in the lower part there are two spines longer than those immediately above them. Cirri, the first pair has the rami unequal, in the proportion of about 19 segments in the longer ramus, to 16 in the shorter. The segments in the latter have their anterior surfaces very protuberant. The second pair is short, with the anterior surfaces of the segments protuberant. On the thorax (Pl. 25, fig. 1), on each side, at the bases of third pair of cirri, there is a projecting membranous plate fringed with fine bristles. The three posterior pairs have their segments shield-shaped in front, generally bearing four pairs of spines, of which the lower pair is minute; between these pairs there are some minute spines. In some young specimens from the Cape of Good Hope, and in var. concinnus, I found six pairs of spines on the segments of the posterior cirri.

Geographical Distribution.—This species is extremely common over the whole of the warmer seas. It ranges from the Island of Madeira to the Cape of Good Hope, and on the west coast of America, from Monterez, in lat. 37° N., in California, to Peru. It is attached to rocks and sub-littoral shells, to floating timber, to kelp, and to Lepas anatifera. It is attached in wonderful numbers to ships' bottoms arriving at our ports, from West Africa, the West Indies, the East Indian Archipelago, and China. It is generally associated with B. amphitrite and amaryllis. I have already stated that, on the bottoms of vessels, the different varieties are generally grouped together; and this makes me believe that they are local. In Mr. Stutchbury's collection there are numerous specimens taken from a ship which first went to the west coast of Africa for guano, and then to Patagonia for the same object, and it was interesting to see the manner in which numbers of B. psittacus, a Patagonian species, had become attached on the African B. tintinnabulum. The varieties from the west coast of America seem eminently peculiar; we there find var. coccopoma and concinnus; and a blueish, rugged variety, with peculiar opercular valves.

Geological History.—I have seen specimens in Mr. S. Wood's collection from the Red Crag of England, which, though not accompanied by opercular valves, I cannot doubt belong to this species. The specimens named by Mr. Sowerby, in the 'Mineral Conchology,' as B. crassus, and which I have seen through the kindness of Mr. J. de C.

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Sowerby, also belong to this species. I further believe that a specimen in Sir C. Lyell's collection, given to him by M. Dujardin under the name of B. fasciatus from Touraine, is likewise B. tintinnabulum.

Varieties.

With respect to var. communis, I have nothing to remark. The second, var. vesiculosus (Pl. 2, fig. 1 h), is confined to young specimens, and may, perhaps, be due to a want of calcareous matter. With respect to var. validus (Pl. 1, figs. 1 c, 1 f infra), I may observe that some of the coarsest and strongest specimens which I have seen were said to have been attached to a surface of iron. I have seen two large lots of var. zebra (1 g), taken by Mr. Stutchbury, from the bottoms of ships, arriving from Bengal and China, and in both cases associated with var. communis, and in one case with var. coccopoma. I at first thought that this variety, zebra, was specifically distinct, but now I feel no doubt, that it is a mere variety; its body was in every respect identical with that of var. communis.

Nor have I any doubt that var. crispatus, of Schröter (Pl. 1, fig. h), is only a variety, although the scuta in some specimens have a peculiar appearance, externally like these valves in var. occator (Pl. 2, fig. 1 b): the scutum is here broader and flatter than in var. communis, and the adductor ridge is very feebly developed, but we shall see how variable this ridge is in all the varieties: externally, the sharp, hood-like points formed by the upturned lines of growth, have a very remarkable appearance, from being arranged in quite straight radiating lines. This structure is evidently caused by the same tendency which produces on the walls the sharp, upturned, irregular points; but it is singular that the scuta are smooth in some specimens with very rough parietes; and, on the other hand, bristling with the symmetrically arranged, hood-like projections, in other specimens on which I could with difficulty detect only a few exceedingly minute points on the walls. In var. communis I have seen a few specimens with a slight tendency in the scuta to become striated longitudinally. The tergum in var. crispatus presents no difference from that in var. communis. Some of the roughest and best characterised specimens of var. crispatus appear to have come off copper-sheathed vessels.

I believe var. spinosus of Gmelin (Pl. 1, fig. i), has been correctly considered by me as a variety, but I have unfortunately seen only one set of specimens with their opercular valves preserved: these were attached to Lepas anatifera. The colour of the shell varies from reddish-purple to nearly white; the radii are sometimes quite white; the walls are slightly ribbed. The scuta in the above specimens, externally were smooth; the adductor ridge was rather more distinct from the articular ridge than in any other variety; and the terga rather more plainly beaked. The tubular, up-curved, calcareous spines sometimes occur only on one side of the shell, and often only in the lower part. These spines are often coloured brighter than the walls. Their presence cannot be accounted for (any more than the state of the scuta in the

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foregoing var. crispatus) by the nature of the surface to which they are attached; for I have seen one set attached to a large rugged specimen of B. tintinnabulum, and another to the very smooth valves of Lepas anatifera. I believe that this form is almost always associated with var. communis, which is an argument that it is only a variety.

To var. coccopoma (Pl. 1, fig. d) I alluded in my introductory remarks as having so strongly the aspect of a distinct species. I possess a beautiful group, with a globulo-conical, smooth shell, of the finest rose colour, with a rather small, rounded orifice. These specimens were attached (mingled with B. trigonus) to Avicula margaritifera, from, as Mr. Cuming believes, Panama. I can never look at this set of specimens without doubting the correctness of the determination at which I have arrived. In the British Museum there are two sets of specimens taken off a vessel, on the west coast of South America, almost identical in external appearance with those in my possession, but rather more rugged. Mr. Stutchbury has sent me some specimens from a ship, direct from China, which are rather paler pink, and more striped, and come near to some ordinary varieties of B. tintinnabulum. The scuta (Pl. 2, fig. 1 f ) in the above three sets of specimens agree in having the adductor ridge more developed, and the pit for the lateral depressor muscle deeper than is usual. The tergum ( 1 l, 1 o) in most, but not in all these specimens, has a rather broader spur; and some of the specimens have the carinal portion of the basal margin considerably hollowed out; the spur, also, is placed nearer the basi-scutal angle than in ordinary cases. On the other hand, in Mr. Cuming's collection, there are two specimens taken off a vessel, identical in external appearance with the foregoing, but which have scuta and terga in every character exactly as in var. communis; hence I am compelled to consider all these specimens as mere varieties.

Var. concinnus (Pl. 1, fig. e) is, perhaps, the most remarkable of all the varieties; I have seen three sets of specimens from the west coast of South America,—all identical in appearance, having longitudinally-ribbed walls, either rosy or of a dull purple, striped and freckled in a peculiar manner with white. I have, however, seen an approach to this colouring in some few specimens of var. communis; and the shell itself offers no other peculiarities. The scutum (Pl. 2, fig. 1 g) resembles, in general shape, that of var. coccopoma; but the adductor ridge is here much sharper and more prominent; and the rostral depressor muscle, instead of being lodged in a little cavity formed by the folding over the occludent margin, has, in addition, a small plate on the under side, which tends to convert the pit into a tube. The tergum exactly resembles that of var. communis. The segments in the sixth cirrus bear six, instead of four, pairs of spines,—a circumstance which I have noticed only in some young specimens of var. communis, from the Cape of Good Hope. From these several peculiarities, until quite lately, I resolved to keep this form specifically distinct; but I have finally concluded that they are not sufficient. For firstly, I have seen a scutum in var. communis (Pl. 2, fig. 1 d), with the adductor ridge nearly as sharp; and this ridge is always strongly pronounced in var. coccopoma; secondly, with respect to the plate for the rostral depressor muscle,

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although I have not seen this in any other variety, yet in Bal. concavus a closely analogous plate, situated in the lateral depressor cavity, is highly variable, and I am not willing to found a new species on one minute point of structure,—a structure which is variable in another species of the same genus.

I have seen some cylindrical and conical specimens of B. tintinnabulum, from the coast of Mexico and California, only noticeable, as far as the shell was concerned, from being rugged, and of a dull blueish-purple; but which had opercular valves exactly like those of var. coccopoma, and therefore, as far as the scutum is concerned, approaching closely in structure to var. concinnus,—all three from the west coast of America. Hence I was at one time led to believe that there existed a species on this line of coast, which represented B. tintinnabulum, and which varied in external shape and colour in an analogous manner to that species. But as the opercular valves in var. coccopoma are sometimes identical with those of var. communis, and as this is always the case with the tergum of var. concinnus, and as the shell itself presents no differences, it is scarcely possible to admit the existence on the west coast of America of this supposed representative of B. tintinnabulum.

With respect to var. intermedius I have little to say in addition to the character given above: I have seen only two groups of specimens in Mr. Cuming's collection: the chief interest in this variety is that it shows that the next form must be ranked as a variety, and not as a distinct species.

Of var. occator (Pl. 1, fig. k) I have seen several specimens, mostly taken off the bottoms of vessels, and one specimen, marked in Mr. Cuming's collection "South Seas." After having carefully examined these specimens, I came to the conclusion, that the slightly oblique radii—the general colouring, and more especially that of the sheath—the scuta (Pl. 2, fig. 1 b), with their sharp hood-like points, in radiating lines—and the terga, with the spur so near to the basi-scutal angle, were amply sufficient to distinguish it as a good species. Subsequently, however, I found that the scuta in var. crispatus presented, both externally and internally, exactly the same peculiar appearance. In var. intermedius, I found the summits of the radii equally oblique, and the general colouring nearly the same, and more especially a close approach to the singular circumstance of the sheath differing in colour towards the opposite ends of the shell. So that the position of the spur of the tergum was the chief remaining character; and this evidently varied considerably in the four or five specimens examined by me, being either its own width, or much less than its own width, from the basi-scutal angle: the outline, also, of the small portion of basal margin, between the spur and the basi-scutal angle, likewise varied much, being either angularly indented, or gradually curved down towards the spur: so also the tip of the spur varied in shape. The longitudinal furrow is unusually apt, in this variety, to remain open. We know that the position of the spur varies considerably in var. communis. Hence, although the spur, on an average, lies closer to the basi-scutal angle in this than in any other variety, even than in

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var. d'Orbignii, it would, I conceive, be preposterous to found a species on this one character. In the animal's body, every part agrees perfectly with that of var. communis.

Lastly, we come to var. d'Orbignii (Pl. 1, fig. l): until quite recently I did not even suspect that this form was only a variety of B. tintinnabulum: I have examined a great number of specimens in Mr. Stutchbury's collection, which had come attached on a vessel from Java, and likewise a few other specimens in other collections. They all closely resemble each other in shape, and even in size, and differ only in tint of colour, and in the surface being either very smooth, or longitudinally ribbed, sometimes with rugged, sharp points. From this circumstance—from the peculiarity of the tint, with the tips of the parietes and one side of the radii perfectly white—and from the obliquity of the summits of the radii, I was led to think this form specifically distinct. But the colour does not differ from that of some other varieties of B. tintinnabulum; the circumstance of the colour being uniform or not striped, is common to the sub-varieties of several varieties, and the white tips to the parietes, and the white borders to the radii, result simply from the shell, whilst young, having been wholly white, and this is not rarely the case with var. communis. Dismissing, therefore, colour, it will be found that hardly any other characters remain by which this form can be separated from var. occator; in both the summits of the radii are oblique, in both the sheath is coloured in nearly the same manner, in both the opercular valves, especially the terga (Pl. 2, figs. 1 m, 1 n), resemble each other; the scuta, however, are smooth in var. d'Orbignii and rough in var. occator. This latter form, certainly, cannot be specifically separated from var. intermedius, and this assuredly is only a variety of B. tintinnabulum. Hence I am led to conclude that Balanus d'Orbignii of Chenu, peculiar as its whole aspect is, must be ranked only as a variety of B. tintinnabulum; its oblique radii resulting from the same cause, whatever that may be, which has given this structure to var. intermedius and occator; and its peculiar colouring to having been exposed (owing probably to having been transported on vessels) to different conditions, whilst young and old.

2. BALANUS TULIPIFORMIS. Pl. 2, fig. 2 a-2 d.

BALANUS TULIPIFORMIS EX CORALLIO RUBRO. Ellis.* Philosoph. Transactions, vol. 50 (1758), tab. 30, fig. 10.

LEPAS TULIPA. Poli. Test. utriusque Siciliæ, tab. 5, fig. 1 et 6 (1791).

BALANUS TINTINNABULUM (var.) Chenu. Illust. Conch., tab. 3, f. 5.

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* According to the letter of the Rules of the British Association, Ellis's name ought to be retained, as it was published in 1758, the same year during which the 10th edition of the 'Systema Naturæ' appeared, in which edition the

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Shell dark rose-coloured, sometimes tinged with purple; orifice toothed. Scutum externally very smooth, covered by membrane. Tergum with distinct crests for the depressor muscles.

Hab.—Sicily, Malta, Malaga, (associated with B. perforatus), Madeira. Often growing in clusters and associated with Pachylasma giganteum. Attached to Millepora aspera, oysters, and other shells. According to Poli, an inhabitant of deep water; yet in mus. Cuming there are two fine specimens attached to the always floating Lepas anatifera. Mus. Lowe, Macandrew, Stutchbury.

General Appearance.—Shell tubulo-conical or conical: orifice large, toothed, approaching to pentagonal. Surface moderately smooth, naked. Colour rosy, or tile-red, with a slight tinge of purple; or beautiful rich purple. Radii nearly as dark as, or darker than, the parietes. The portion of the alæ seen externally is generally white. Internally the whole shell is nearly white. Generally the tints outside vary in transverse fasciæ; sometimes there are very fine, dark, longitudinal lines. Largest specimen (from Malta), 1.4 of an inch in basal diameter; usually full-sized specimens are about three quarters of an inch in basal diameter.

Scuta (Pl. 2, fig. 2 a, 2 c) very smooth, with the growth-ridges very little prominent, sometimes there are obscure traces of longitudinal striæ; surface covered by an unusually thick and persistent yellow membrane: valve narrow, with the upper part commonly reflexed: the basal margin forms, with the occludent margin, a smaller angle than is usual: the tergal margin of the valve is rectangularly inflected, instead of being, as is usual, merely bowed inwards. Internally, the articular ridge is rather prominent. The depth of the slight pit for the lateral depressor muscle is variable; it sometimes includes a minute, central, longitudinal ridge.

Terga (2 b, 2 d): the longitudinal furrow is deep, with the sides folded in; the spur is placed at about its own width from the basi-scutal angle; it is moderately long, with its lower end obliquely rounded off; but the length, breadth, and precise outline of the lower end varies a little. The basal margin on the opposite sides of the

binomial method was first used. But as Ellis himself did not then know of, or follow this method, it might be disputed whether, according to the spirit of the law, his name ought to stand. The only other name given to this species is that of tulipa, affixed by Poli in 1791, but this name had been previously used by Müller in 1776, and by Chemnitz in 1785, for another species, the B. Hameri of this work; and likewise, also previously to Poli, by Bruguière in 1789, for still another species, viz., B. tintinnabulum of this work: under these complicated causes of confusion, I think it is highly advisable to adopt Ellis's name. I may add that the B. tulipa of Mr. G. B. Sowerby is the B. tintinnabulum of this work. It is possible that the B. conoides of Brown, 'Illustrations Conch.' (1st edit. pl. 6, fig. 7), may be our present species; but without details of structure it is hardly possible to identify, in many cases, the species of Balanus.

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spur, forms a nearly straight line, but with the portion on the carinal side very slightly hollowed out. Crests for the depressor muscle are well developed.

Compartments.—The radii and alæ always have their summits oblique: the sutural edges of the radii are deeply penetrated by pores between the strongly denticulated septa: the sutural edges of the alæ are quite smooth: the tubes in the parietes are crossed in the upper part of the shell by septa. Basis tubular, with an underlying cancellated mass.

Mouth.—Labrum with the teeth either absent or very small: mandibles with the fourth and fifth teeth rudimentary: maxillæ with a small notch under the two upper spines; near the lower angle, two spines, one beneath the other, are larger even than the upper pair; beneath the lower pair, there is a tuft of fine spines. Cirri, segments protuberant in one ramus of the first cirrus and in both rami of the second cirrus; posterior cirri with the segments short and broad, each bearing three pairs of spines, with a small intermediate tuft.

Affinities.—This species in all essential respects comes very near to the three last varieties of B. tintinnabulum, which have the orifices of their shells toothed. The smoothness of the scutum, with its persistent epidermis,—its peculiar shape,—its small and not reflexed articular ridge,—together with the crests on the tergum for the depressor muscles, are sufficient diagnostic characters. Even in general habit and tint of colour, this species has a different aspect from B. tintinnabulum. In some respects B. tulipiformis leads into the species included in the third section of the genus.

3. BALANUS PSITTACUS. Pl. 2, fig. 3 a-3 d.

LEPAS PSITTACUS. Molina. Hist. Nat. Chile (1788), vol. i, p. 223.

BALANUS PICOS. Lesson. Zoolog. Voyage de la Coquille (1829).

— TINTINNABULUM (var. c.) Ranzani. Mem. di Storia Nat. tab. 3, fig. 1-3 (1820).

— CYLINDRACEUS. Lamarck, in Chenu. Illust. Conch. Tab. 4, fig. 17, Tab. 5, fig. 7, sed non var. (c.) in Lamarck, Animaux sans Vert., (1818).

— PSITTACUS. King and Broderip. Zoolog. Journal, vol. v (1832-1834), p. 332.

Shell, pale dirty pink; orifice hexagonal. Scutum with the articular ridge very small, confluent with the very prominent adductor ridge, forming a tubular cavity, which extends up to the apex of the valve. Tergum with the apex produced, needle-like, purple: spur placed at less than its own width from the basi-scutal angle.

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Hab.—Peru, Chile, Chiloe, Patagonia. Fossil in an ancient tertiary deposit, Coquimbo; and in a superficial, recent bed at S. Josef, in Patagonia.

General appearance.—Shell either almost cylindrical or steeply conical, generally flesh-coloured, sometimes pale pink; surface either smooth (when not disintegrated) or sometimes with the parietes distinctly and rather strongly ribbed, with the ribs distant from each other: I have seen six or seven ribs on the rostrum alone. The orifice in the most perfect specimens is nearly equilateral and hexagonal. The radii generally are very broad, but occasionally quite narrow, and even linear. The basis is generally deeply and irregularly cup-formed.

Size.—This is the largest species in the family: I have seen a specimen six inches in length and three and a half in diameter; and another specimen no less than nine in length, though only two and a half inches in diameter.

Scuta.—In full-sized specimens the surface is finely striated longitudinally, caused by the lines of growth being minutely sinuous; but in young specimens, until they attain a basal diameter of above half an inch, the surface is smooth. The valve is transversely arched, a line of flexure running from the apex to the basal margin, at about one third of the width of the valve from the tergal margin. The basal margin is curved nearly continuously, and extends nearly half-way up the valve; hence the basi-tergal corner is largely rounded off. The articular ridge is but little prominent, and is not reflexed: the articular furrow is very narrow. The adductor ridge consists of a sharp, much-projecting plate, running down close to the basal margin, and is confluent with the lower part of the articular ridge. This plate and the inflected tergal margin of the valve, together form a large and deep cavity, which extends up almost to the apex of the valve. The depressor muscle is attached in the middle, at the lower, open end of this cavity.

Terga.—These are strongly beaked, the beak being from one third to one fourth of the total length of the valve, including the spur: the beak is very sharp, somewhat flattened, and bowed; when young, and when well preserved, it is coloured purple: it is penetrated by a fine tubular cavity, occupied by a thread of corium, which extends about half-way up it. The whole valve is narrow, being about thrice as long as wide. The spur is also long and narrow; it is seated at less than its own width from the basi-scutal angle. The scutal margin is not much inflected. The longitudinal furrow has its sides, in full-grown specimens, closely folded together. The basal margin slopes down on both sides to the spur. There are no crests, or only traces of them, for the attachment of the depressor muscle. Internally, the spur is prolonged, as a prominent ridge, upwards to the beak, and serves as an articular ridge. In the middle, in the upper part (Pl. 2, fig. 3 d), between this articular ridge and the carinal margin, there is a second narrow ridge, which extends from the lower part of the beak half-way down the valve, and then dies out. The space between these two ridges, and the ridges themselves, are coloured purple, and consist of

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harder shell than the rest of the valve; hence, when the outer surface and the adjoining scutal and carinal margins disintegrate, this part remains, and so forms the beaked, purple apex.

Compartments.—The parietal tubes are unusually large in proportion to the size of the shell, and run up to the summit without any transverse septa: the longitudinal septa are strongly denticulated. The radii are penetrated by large tubes; their septa are very strongly denticulated, and the denticuli themselves often subdivide and branch out at their extremities. The sutural edges of the alæ are smooth, or with a high power can just be seen to be crenated. The radii are generally very highly developed, so that their summits are even wider than the bases of the parietes; but, on the other hand, in some few large specimens, the radii are either very narrow or absolutely linear. In these latter cases, the diametric growth has nearly or altogether ceased, whilst the walls of the shell have continued to be added to at their bases, their summits at the same time suffering disintegration; and thus the orifice has increased in size.

Basis generally, and occasionally very deeply, cup-formed. An unusually thick cancellated layer in most cases forms the under side of the basis.

Mouth.—Labrum apparently without teeth, or with very minute ones: mandibles with three teeth, of which the third is thicker than the first or upper one: the fourth and fifth teeth are confluent with the inferior angle. The maxillæ have a small notch under the upper pair of spines; inferior part projecting and supporting two spines, placed one below the other, and equalling in size the upper pair. Cirri: the rami of the first cirrus are unequal by four or five segments; shorter ramus and both rami of the second cirrus with the segments extremely protuberant: posterior cirri not much elongated, with the segments rather broad, supporting six pairs of spines.

General Remarks.—This, which is much the largest known species of the genus, ranges from Peru (Arica being the most northern spot, whence I have seen specimens), along the coast of Chile, where it is very abundant at a few fathoms' depth, at least as far south as Southern Chiloe; it is said by Captain King to attain the largest size at Conception. On the coast of Eastern Patagonia, I dredged up this species from nineteen fathoms, in lat. 49°. In lat. 42° (S. Josef), on the same eastern coast, I found fossil specimens in beds of sand upraised between eighty and one hundred feet. In the tertiary formation at Coquimbo, in Chile, it occurs in the middle bed, associated with the recent B. lævis, and with various mollusca, all of which are apparently extinct, indicating that the formation is of considerable antiquity. In the living state, on the coast of Chile, it is often associated with B. lævis. As it frequently adheres to large specimens of the Concholepas, it must sometimes be an inhabitant of shallow water. I have seen one specimen attached to Mytilus Magellanicus. Mr. Cuming believes that about six fathoms is the usual depth at which it lives. Numerous specimens are often congregated together into great masses. Mr. Stutchbury has some interesting specimens which he procured from a ship that had first sailed to Ichaboe, on

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the coast of Africa, and afterwards to Patagonia; consequently numerous specimens of B. psittacus had become attached on B. tintinnabulum, and subsequently during the voyage home, some few of the latter again had adhered on B. psittacus: the contrast in the paler colour and hexagonal orifice of this species, with the darker tints and more trigonal orifice of B. tintinnabulum was striking. At Coquimbo, in Chile, I procured a specimen of B. psittacus, attached to a chain cable which had been in the water only six months; this specimen measured 1.3 of an inch in basal diameter, and .8 in height: this shows a rapid rate of growth. Lastly, I may mention that it is asserted by Molina, and I am assured by Mr. Cuming that the statement is perfectly correct, that this Balanus, when cooked, is universally esteemed as a delicious article of food.

4. BALANUS CAPENSIS. Pl. 2, fig. 4 a, 4 b.

BALANUS CAPENSIS ORE OBLIQUO. Ellis. Phil. Transact., vol. 50 (1758), Tab. 34, fig. 14.

Shell shaded, and often longitudinally striped with bright pink. Scutum as in B. psittacus. Tergum with the apex produced and needle-like, white: spur placed at its own width from the basi-scutal angle.

Hab.—Cape of Good Hope. Attached to stems of Fuci, Algoa Bay. Mus. Brit. and Bowerbank. Attached to a Patella, Mus. Darwin, Mus. Cuming, and Stutchbury. Attached to floating kelp, Lagulhas Bank, Mus. James Ross, associated with B. tintinnabulum and spongicola.

This species comes extremely close to the South American B. psittacus, and I should hardly have attached a specific name to it, had I not examined many specimens, young and old, of the true B. psittacus, from Peru, Chile, and Eastern Patagonia, and found them all identical in the few, apparently trifling points, in which that species differs from B. capensis. The animal's body and the shell agree in every respect, excepting that the shell is decidedly pinker, being often most distinctly and prettily striped longitudinally with pale and bright pink. In some of the specimens the basis is cup-formed: in some, the broad radii are pale pink, in others they are quite white, and in this latter case a singular aspect is given to the pinkish varieties. In very large specimens (and I have seen one fully two inches in basal diameter) the pink colour is extremely feeble, and the whole shell has a very rugged, disintegrated, coarse, and sometimes dirty appearance: in most of these large specimens the walls are more massive than in B. psittacus, and the orifice of the shell rather smaller; in some, however, the walls certainly are of unusual thinness.

The Scuta differ from those of B. psittacus only in the basi-tergal

14                          

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corner not being so much rounded off, and consequently in the articular ridge, which is rather more reflexed, descending in proportion lower down the valve: the cavity at the basi-tergal corner is in proportion broader. The valves in the two species differ, also, but only in young specimens, in the occludent half being tinted, both externally and internally, purple, whereas in B. psittacus the whole valve, at all ages, is white. In the terga the spur is removed fully its own width from the basi-scutal angle, whereas it is not half this distance in B. psittacus. The scutal margin is here much more inflected. In B. psittacus there is a remarkable patch of purple on the inside of the valve, between the articular ridge and a second special ridge; of this purple patch there is here no trace, consequently the beak or apex is white. The beak, also, is less prominent. The special ridge, just alluded to, here runs much nearer to the articular ridge, and is less prominent: indeed, in old specimens, it is often almost obliterated. Finally, the whole valve, in proportion to the scutum, is rather broader.

I have seen a young specimen, about a quarter of an inch in basal diameter, with the orifice of the shell toothed owing to the obliquity of the summits of the radii; and this gave the shell a very peculiar aspect. The largest well-coloured specimen which I have seen is 1.2 of an inch in basal diameter; but in Mr. Cuming's collection there are two rugged, disintegrated specimens, two inches in basal diameter, and two and a half in height. Some specimens, 1.3 in basal diameter, in Mr. Stutchbury's collection, are remarkable from the radii having been obliterated—the shell being merely divided by six sutures, as we have seen is likewise sometimes the case with large specimens of B. psittacus.

This species is evidently a South African representative of the South American B. psittacus.

5. BALANUS NIGRESCENS. Pl. 2, fig. 5a, 5 b.

BALANUS NIGRESCENS. Lamarck, (1818) in Chenu. Illust. Conch., Tab. 4, fig. 16.

— GIGAS. Ranzani. Memoire di Storia Nat., 1820, Tab. 3, fig. 5, 6, 7.

— — De Blainville. Dict. des Sc. Nat., Tab. 116, fig. 2, 2 a.

Shell cinereous, tinted with pale or blackish blue, or wholly white. Scutum with the articular ridge terminating downwards in a small, sharp, free point: adductor ridge prominent. Tergum with the apex produced and needle-like.

Hab.—Swan River, West Australia, Mus. Brit., attached to sandstone. Attached to sandstone and to each other in a group, Mus. Cuming. Twofold Bay, S. E. Australia, attached to tidal rocks and Patellæ, Mus. Darwin.

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There can be no doubt that this species is the B. nigrescens in Chenu, who had access to Lamarck's original specimens; and there can be equally little doubt that it is the B. gigas of Ranzani, collected, during Baudin's expedition, at King George's Sound: it is essentially allied to B. psittacus, but in external appearance strikingly resembles some of the varieties of B. tintinnabulum.

General Appearance.—Shape tubulo-conical: walls smooth, sometimes longitudinally ribbed: colour ashy-grey tinged with blue, but many specimens are dark purplish-blue, owing to the disintegration of the outer lamina, and consequent exposure of the almost solidly filled up, dark blueish parietal tubes; on the other hand, some specimens are quite white. Ranzani describes the colour as earthy-violet, which is very characteristic of some of the specimens. The orifice is apt to be rather small, compared to the size of the specimens, and tends to be hexagonal. The radii are often rather narrow. The opercular valves are tinted pale blue. The basal diameter of the largest specimen is two inches, and its height two and a quarter.

The Scuta have their basi-tergal corner much rounded off, as in B. psittacus, so that the tergal margin does not extend more than half down the valve. The surface is somewhat prominent, along a line runing from the apex to the point of chief curvature in the basal margin. The surface is not striated. Internally, the articular ridge is little prominent, and not reflexed; the lower end depends as a free, sharp style or point. The adductor ridge is moderately sharp, and stands some little way distant from the articular ridge: it is produced downwards, and forms a moderately deep and large cavity for the depressor muscle; but this cavity is not closed, and does not extend up, as in the two last species, to the apex of the valve.

Terga, narrow, with a sharp, prominent, needle-like beak. Spur, long, narrow, placed at less than its own width from the basi-scutal angle: the basal margin on both sides slopes down to the spur: the scutal margin is not inflected. Internally, the articular ridge is very feebly developed, but extends down close to the basi-scutal angle. On the under surface in the upper part of the valve, there is a short, very slight ridge, extending on the carinal side, near and parallel to the articular ridge; this slight ridge plays an important part, as in the two foregoing species, in the formation of the beak or apex. Crests for the depressor muscle are hardly distinguishable.

The Walls appear to vary in some degree in strength and thickness; as is likewise the case with the opercular valves. In some of the thinner specimens, the parietal tubes are large, and the longitudinal septa are furnished with small, sharp denticula. The tubes are often thickly lined or almost filled up solidly with blue shell; they are not crossed by transverse septa.

The Radii vary in width; externally they are often finely ribbed transversely, at other times they are smooth; their septa are fine and

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thin, with their delicate denticuli not extending to the outer lamina: they are very porose. The alæ have their summits parallel to the basis; their sutural edges are most finely crenated. The sheath is blueish, excepting the wedge-like portions of the alæ which have been added during the diametric growth, and these are white.

Mouth: labrum without teeth: mandibles with five sharp teeth: maxillæ with the edge straight. Cirri, first pair with the rami very slightly unequal; segments of the shorter ramus and of both rami of the second pair protuberant: posterior cirri with the segments shield-shaped in front, bearing four pairs of spines, of which the upper pair is much longer than the lower pairs; each pair has a small intermediate tuft of minute spines.

6. BALANUS DECORUS. Pl. 2, fig. 6 a, 6 b.

Parietes pale pink; radii rather darker. Scutum with a small articular ridge. Tergum with the longitudinal furrow very shallow and open; basal margin on both sides sloping towards the spur.

Hab.—New Zealand. Mus. Brit., and Flower: attached to shells.

General Appearance.—Shell conical or tubular, with a large rhomboidal orifice; very pale pink, but tinted yellowish from the persistent epidermis, and sometimes faintly striped longitudinally; radii and sheath of rather a darker pink; scuta in themselves white, though lined by purple corium; the carinal half of the tergum pink. Walls extremely smooth. Largest specimen above one inch in basal diameter.

Scuta, with the finest striæ radiating from the apex; growth-ridges moderately prominent; articular ridge small; there is a very slight and blunt adductor ridge: the hollow for the lateral depressor muscle is rather narrow and deep.

Terga, with the apex slightly prominent or beaked; the longitudinal furrow is of very little depth; on its scutal margin there is a narrow, rounded, slightly prominent ridge, which, however, appears more like a furrow than a ridge. Spur moderately long and blunt; placed at half its own width from the basi-scutal angle; the basal margin on both sides of the spur, slopes gently towards it. Internally, the articular ridge is pretty well developed; the scutal margin is not much inflected; the carinal portion of the under surface of the valve is rough; the crests for the carinal depressor muscle are entirely absent.

Compartments.—Walls moderately strong; parietal tubes small, with transverse septa in their upper ends; inner surface of the walls much less strongly ribbed than is usual. Radii broad, with their summits parallel to the basis; their septa are strongly denticulated. Alæ

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with their summits oblique; their sutural edges are barely crenated. Basis, thin, flat, or cup-formed. Body unknown.

Affinities.—In general appearance this species comes near to B. psittacus; but in all essential characters it comes much closer to the following species, from which, however, it can easily be distinguished by colour, and by the inner lamina of the parietes not being cancellated.

7. BALANUS VINACEUS. Pl. 2, fig. 7 a-7 d.

Shell purplish dark brown: inner lamina of the parietes cancellated. Scutum finely striated longitudinally. Tergum with the longitudinal furrow shallow and open; basal margin on both sides sloping towards the spur.

Hab.—West Coast of South America. Mus. Cuming.

General Appearance.—Shell conical, with a large, rhomboidal orifice; walls rather thin, coloured, together with the radii and operculum, dark purplish-brown; sheath nearly colourless. Walls smooth, slightly irregular, very finely striated longitudinally. Basal diameter of largest specimen .8 of an inch.

Opercular Valves, unusually smooth, that is without prominent growth-ridges. Scuta, finely striated longitudinally, with the sharp striæ closely approximate. The teeth on the occludent margin are sharp, and stand some way apart from each other. Internally, the whole surface is remarkably flat and smooth: the articular ridge is of moderate breadth, and slightly reflexed: there is no adductor ridge, and the oval depression for the lateral depressor muscle is extremely slight. Terga, with the longitudinal furrow very slight; the bottom of this furrow is feebly striated longitudinally, and there is a trace of a fine, rounded ridge on the scutal margin, as in B. decorus. The basal margin slopes on both sides towards the spur, which is of moderate length and breadth, with its lower end truncated and parallel to the carino-basal margin; the spur stands at about once and a half its own width from the basi-scutal angle. Internally, the valve is lined by very dark, purplish-brown corium; the articular ridge is prominent; in the upper part of the valve, parallel to the articular ridge, there are two or three feeble ridges; there are no crests for the tergal depressores.

The Parietes, though moderately thick, yet are light and fragile; the denticuli at the bases of the longitudinal septa are prominent, and those on the adjoining septa are united together, making a net-work (Pl. 2, fig. 7 d), but the interspaces between them are not filled up by solid calcareous matter (as is the case with every other species of the genus), but are only crossed at successive levels by fine transverse calcareous septa; the internal lamina thus becoming cancellated, and, though thick, fragile. Hence, in a transverse section of the parietes, the ordinary parietal tubes or pores are seen to be lined on their inner sides

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by five or six rows of very minute pores. I have not seen any other instance of this structure. The internal lamina is ribbed, as usual, on its inner surface, by the projection of the longitudinal septa. The ordinary parietal tubes are open, to nearly the summit of the shell. The radii are rather thin, and unusually fragile; their summits are parallel to the basis: their septa, as seen on the sutural edges, are extremely thin and denticulated on both their upper and lower surfaces, on the side towards the internal lamina: towards the external lamina, the septa are simple, and the small square pores thus formed, are open or not filled up. The alæ have their summits extremely oblique, being added to very little during the diametric growth of the shell; the narrow margin, however, which is thus added, is coloured red, the rest of the sheath being nearly colourless: the sutural edges of the alæ are smooth. The basis has a thick, underlying, finely cancellated layer of shell.

Animal's body unknown.

A young specimen, .2 of an inch in basal diameter, differed from the above in being of a much paler purplish-brown. This species is distinct from all its congeners, in its peculiar colour, and likewise in the structure of the inner lamina of the parietes. As already stated, it comes nearer to B. decorus than to any other species.

8. BALANUS AJAX. Pl. 3, fig. 1 a-1 d.

BALANUS TINTINNABULUM (var.) Chenu. Illust. Conch., Tab. 2, fig. 8.

Shell globulo-conical, often elongated in the rostro-carinal axis, pale pink, smooth, extremely massive: parietal pores, close to the basal margin, circular and very small. Scutum with the articular ridge broad and reflexed.

Hab.—Philippine Archipelago, attached to Millepora complanata, Mus. Cuming. Mus. Brit. and Stutchbury.

General Appearance.—Shell globulo-convex, sometimes much elongated in its rostro-carinal axis; smooth; walls excessively strong, massive, and heavy. Orifice oval, rather small in proportion to the size of shell, this being chiefly due to the infolding of the upper part of the rostral compartment. Parietes pale pink, feebly tinted with purple: radii either paler, or tinted of a bright chesnut-brown: sheath rich purplish chesnut-brown. Basal diameter of the largest specimen nearly 3 1/2 of an inch; height 2 3/4: another specimen had a basal longitudinal diameter of 2.9 of an inch, and a transverse diameter of only 1.6; this great difference in the two diameters being caused by the prolongation of the basal portion of the rostrum in the line of the branch of the Millepora, to which the shell had adhered; the height of this same specimen was

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1.5; and the diameter of the orifice, both transversely and longitudinally, .75 of an inch.

Scuta, broad, feebly tinted with pink; exterior surface rough, with sharp hood-formed projections, arranged in straight lines radiating from the apex; an inflected portion of the valve along the tergal margin is not roughened. Internally (Pl. 3, fig. 1 d), the articular ridge is broad and reflexed. An adductor ridge can hardly be said to exist, but a slight prominence borders the gentle hollow in which the lateral depressor muscle is attached. The basal margin, on its inner face, is slightly toothed. Tergum white, with the narrow part of the valve, on the scutal side of the spur, rough with the little projecting hoods, like those on the scutum; the other and larger half is smooth; spur rather long, narrow, placed at twice its own width from the basi-scutal angle; on the carinal side, about half of the basal margin slopes down towards the spur. The longitudinal furrow is either quite or nearly closed. Internally, the spur is produced upwards on the valve, as a prominence: the articular ridge is not very prominent. There are no crests for the tergal depressor muscle.

Altogether the opercular valves strikingly resemble those of B. tintinnabulum, but all the characters above mentioned have not been observed in any one variety of this species; perhaps var. coccopoma comes nearest, both in the external appearance of the shell and in the structure of the opercular valves, to B. Ajax.

The Compartments are remarkably compact and solid; the parietal tubes are cylindrical and quite minute even close to the basis; they extend, however, nearly up to the top of the shell; the parietal septa at the basis are thick, and with blunt denticuli; the thickness of the walls in the upper part of the shell is excessive; in the lower part, it is also unusually great, owing to the thickness of the inner lamina, and hence the ribs, generally formed by the projection of the longitudinal septa on the inner lamina, are here visible only close to the basis. The radii are rather wide; their summits are parallel to the basis; the septa on their sutural edges are thin, straight, and closely approximate, and most symmetrically furnished with little denticuli of equal sizes on both sides: the interspaces are nearly filled up solidly, but with some pores still left open. In the upper part of the shell, the radii, like the walls, are of extraordinary thickness: the septa are transverse and horizontal, as seen externally by slight variations in the colour of the radii; internally, as seen in a vertical section of the shell, the septa dip inwards at an angle of above 45°. The alæ are thin, and have their summits oblique: their sutural edges are smooth. The pores in the basis are crossed by numerous transverse septa, and there is an underlying cancellated layer: the internal surface is very smooth.

Animal's body unknown.

The strength of this Balanus is truly remarkable; and when, by repeated blows, a specimen which I was examining at last yielded, the radii broke sooner than separate at their sutures. In most of its characters, this species approaches B. tintinnabulum, and I believe has been included by Chenu as one of its varieties; but it comes almost equally near to B. stultus, to which it is much more closely allied in

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its habit of being attached to Milleporæ. By a close and unbroken chain of affinities, B. Ajax, through B. stultus, is connected with B. calceolus and its allies in section (B), which live attached to Gorgoniæ. Some of the specimens of B. Ajax, are almost as much elongated in their rostro-carinal axis, as are the species in section (B); and there is an affinity in the same direction in the smallness of the pores in the radii of B. Ajax; indeed, had the basis in this species been generally more boat- or cup-formed, I should have placed it as the first species in section (B), instead of, as at present, the last species in section (A). The intermediateness of the characters of B. Ajax has been one chief cause why I have rejected the genus Conopea, which was instituted by Say for the species living attached to Gorgoniæ.

Section B.

Parietes and basis sometimes permeated by pores, sometimes not: radii not permeated by pores: shell elongated in its rostro-carinal axis: basis boat-shaped: attached to Gorgoniæ and Milleporæ.

——————

9. BALANUS STULTUS. Pl. 3, fig. 2 a-2 d.

Parietes and base porose: shell white, or faintly tinged with purple. Scutum with the basal margin protuberant in the middle. Tergum with the longitudinal furrow closed in the upper part: spur not closely adjoining the basi-scutal angle.

Hab.—Attached to Milleporæ, Singapore, Mus. Cuming. West Indies,* Mus. Brit.—Mus. Stutchbury.

I have considerable doubts whether it would not have been more correct to have placed this species in the last section, instead of where it now stands; it certainly is more

* This specimen in the British Museum was purchased at the sale of the Rev. L. Guilding's collection, and therefore it is not certain that this habitat is correct; but as it was sold in the same lot with a Cirripede certainly West Indian, and as the main collection was made in the West Indies, this habitat may, I think, be trusted.

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closely allied to B. Ajax, especially in its operculum, than to the following species; yet the fact of the radii not being permeated by pores does not permit of its admission into the last section; and both in habits and structure it undoubtedly comes very near to the following species. Those varieties which are not much elongated, and which have the basis nearly flat, would certainly, if considered by themselves alone, not have gained admission into our present section.

General Appearance.—Shell conical, somewhat globular, more or less elongated in the rostro-carinal axis, owing to the basal production of the rostrum. Orifice, rather small, entire, oval, pointed at the carinal end. Radii moderately broad, with their summits parallel to the basis. Colour dirty white, often faintly tinged with purple; sheath, pale purplish-blue. Surface extremely smooth; the parietes are generally covered (as viewed through a lens) by a very thin, yellowish epidermis, giving to the whole a glistening, granular aspect: the radii are generally destitute of this epidermis, and are therefore of a dead white. The basis is concave, and sometimes deeply cup-formed; it is, however, not symmetrical; sometimes it is flat. Basal diameter of largest specimen, including the basis itself, 1.5 of an inch in the longitudinal axis; transverse diameter, 1 inch; the inequality in the length of the two diameters is rarely so great as in this unusually large specimen.

Scuta, externally very convex, with the growth-ridges extremely prominent; basal margin sinuous, the middle portion being prominent; this is best seen in young specimens (Pl. 3, fig. 2 d). Internally, the articular ridge is broad and reflexed. The adductor ridge in the upper part is almost confluent with the articular ridge; it runs down to the most prominent point of the basal margin; in young specimens it is sharp and prominent; in old specimens it is very blunt and little prominent. There is a rather deep hollow for the lateral depressor muscle. In young specimens there is a small, depending, blunt tooth at the basi-tergal angle, which helps to make the basal margin more deeply sinuous.

Terga, with the longitudinal furrow closed, except on the spur itself, where it is open. The spur is moderately long and broad, but varies in breadth; it is placed at rather less than its own width from the basi-scutal angle; its lower end is obliquely rounded; the basal margin on the opposite sides of the spur, together form a nearly straight line. The whole valve is rather broad. The crests for the tergal depressores are barely developed.

The Compartments have rather large parietal tubes; the septa are coarsely denticulated at their bases; the internal lamina is smooth, except close to the basis. The radii have their summits parallel to the basis; their sutural edges are formed of rather thick septa, which stand at an unusual distance apart from each other, and have perfectly symmetrical, minute denticuli on each side. The interspaces between the septa are filled up solidly to within a short distance of the surface; but yet not so

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completely as in the following species, and as in those in the succeeding sections of the genus; this is what might have been expected from the close affinity of B. stultus to B. Ajax, in which latter the radii are still permeated by pores, though smaller than is general in the species of our first section (A). The alæ have their summits extremely oblique, and their sutural edges, I believe, smooth. Basis porose, with an underlying, finely-cancellated layer.

Mouth: labrum with six small teeth; mandibles with the 3d tooth blunt; the 4th minute, and the 5th almost confluent with the inferior angle. Maxillæ with the edge straight and simple. Cirri partly destroyed; on each segment of the sixth pair there were five pairs of spines.

10. BALANUS CALCEOLUS. Pl. 3, fig. 3 a-3 e.

BALANUS CALCEOLUS KERATOPHYTO INVOLUTUS (?) Ellis. Phil. Trans., vol. 50 (1758), Tab. 34, fig. 19.

LEPAS CALCEOLUS (?) Pallas. Elench. Zooph., p. 198, (sine descript.) (1766).

CONOPEA OVATA (?) J. E. Gray. Annals of Philosophy, vol. x, 1825.

Parietes and basis porose. Scutum with the pit for the lateral depressor muscle small and deep.

Hab.—Attached to Gorgoniæ, West Coast of Africa. Tubicoreen, near Madras, (Dr. Johnston), associated with B. navicula. Mediterranean (?). Mus. Brit., Cuming, Stutchbury.

Fossil. Coralline Crag; Mus. S. Wood.

I must premise, with respect to the nomenclature of this and the three following quite distinct species, that in the published descriptions no allusion is made to any one of the characters by which alone they can be distinguished: hence I have been guided by geographical probabilities in assigning the specific name of calceolus to the present species, as Ellis's specimens came from the Mediterranean; and that of galeatus to the North American and West Indian specimens, as Linnæus' original specimens (according to a statement by Spengler) came from the West Indies. I have assigned new names to the two remaining East Indian species. I may here add that Spengler ('Skrifter af Naturhist.' 1 B, tab. 6, fig. 3, 1790) has described, under the name of B. cassis, an allied form attached to the Gorgonia placomus from the seas of

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Norway; but I do not believe that it is the same with our present species.

General Appearance.—The degree of elongation of the shell in the rostro-carinal axis varies considerably (3 a, 3 b): the elongation is due to the production of the rostrum and of the corresponding end of the basal cup. These two portions of the shell always form together an angle, and sometimes an acute angle, whereas in all the many specimens which I have seen, the carina and the carinal end (or heel) of the basis together form a straight line; yet I should not be surprised if this end of the shell was sometimes produced. The surface of the shell is smooth, or sometimes marked with very minute projecting points: it is almost always covered by the horny bark of the Gorgonia. The colour is either dull purplish-red or dull purple, with obscure longitudinal stripes, and often more or less transversely banded with white. The rostrum is either white or very feebly tinted, being always paler than the rest of the shell: the radii are usually paler than the parietes, and are sometimes white: the carinal end of the basal cup is tinted of the same colour with, but rather paler than, the compartments. The orifice is rather small compared to the shell, and nearly heart-shaped. The carino-lateral compartments are about one-third of the width of the lateral compartments. The shell is very strong, and the sutures resist the action of boiling caustic potash. The largest specimen which I have seen was .7 of an inch in extreme length, and under .25 in extreme breadth.

Structure of the shell and basis.—The parietes are permeated by quite distinct pores,—a character sufficient by itself to separate this from the following species; the longitudinal septa forming the tubes are slightly denticulated at their bases. The radii have their summits quite square, extending from apex to apex of the adjoining compartments. The alæ have oblique summits. The sutural edges of the radii have approximate septa, which are obscurely denticulated: the interspaces are filled up solidly, so that the radii are not porose. The basis is distinctly porose, by which this species can be distinguished from B. navicula and cymbiformis. The basis has a deep furrow on the under side, from clasping the thin horny axis of the Gorgonia: the basal point of the rostrum is also notched from the same cause, and, as a consequence, its upper surface becomes slightly furrowed along its whole length.

The Scuta have an articular ridge but moderately prominent, and only slightly reflexed; the basi-tergal corner is rounded off; there is no adductor ridge; there is a small, rather deep, distinct pit for the lateral depressor muscle. Terga; externally the surface is considerably depressed in the line of the spur. The spur is between half and one-third of the width of the valve: its lower end is square and truncated, or in some degree rounded; it is sometimes (3 e) dentated with a few, minute, sharp teeth. The articular ridge is but slightly developed; the crests for the depressor muscle are very feeble.

Animal's body unknown.

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11. BALANUS GALEATUS. Pl. 3, fig. 4 a-4 c.

LEPAS GALEATA (?) Linnæus. Mantissa altera Holmiæ, 1771.

CONOPEA ELONGATA. Say* Journal of Acad. Nat. Sci. Philadelphia, vol. ii, part 2, p. 323, 1822.

Parietes not porose; basis porose. Tergum, with the apex square, caused by the great development of the articular ridge.

Hab.—Charlestown, South Carolina; Florida; West Indies; Central America; attached to Gorgoniæ; Mus. Brit., Agassiz, Cuming, Stutchbury.

General Appearance.—This and the two following species come so close in general appearance to the last, that it will be quite superfluous to do more than describe the few points of difference. The shell and basis are generally quite as much elongated as in the last species, and sometimes much more so, owing to the carinal end (fig. 4 a), with the corresponding portion of the basal cup, being produced like the rostral end, into a flattened, sharp point: I have seen a specimen in this state .9 of an inch in length, and only .25 in breadth in the broadest part. In many specimens, however, the shape is exactly as in B. calceolus; but the rostrum seems less usually furrowed from clasping the stem of the Gorgonia. The colour is paler, pinker, and more distinctly striped longitudinally than in B. calceolus; I have, however, seen some not striped, purple specimens (and one transversely freckled with white) from the West Indies. The parietes are strongly-ribbed internally, and are not permeated by pores. The radii have their sutural edges crenated. The basal cup is permeated by pores.

The Scutum differs from that in the last species, only in the pit for the lateral depressor muscle, being much shallower, and less defined, and in the apex being truncated. The Tergum is remarkable from its broad, square, truncated summit, which underlies the whole broad apex of the scutum: the square summit of the tergum is formed by a great and peculiar development of the uppermost part of the articular ridge. The spur is a little narrower than in B. calceolus.

Mouth: on the crest of the labrum there are two teeth on each side of the central notch. The mandibles have five teeth, of which the two lower are very small. The maxillæ show a trace of a notch under the upper large pair of spines; near the inferior angle there are two long spines. Cirri: in the first pair, one ramus is nearly twice as long as the other: the segments are not very protuberant. There is a sharp point at the dorsal basis of the penis. The branchiæ are of moderate size, and plicated on one side.

—————————————————————————————————————————————

* If I have assigned the specific title of galeatus to the wrong species, yet Say's name of elongatus ought not strictly to be admitted; as the Lepas elongata of Gmelin is a Balanus,—probably a variety of Balanus crenatus. I may add, that as the Lepas galeata of Schröter ('Einleitung in die Conch.' &c.), was attached to a Gorgonia from the East Indies, it cannot be our present species, but probably is one of the three other allied species, which all occur in India.

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12. BALANUS CYMBIFORMIS. Pl. 3, fig. 5 a, 5 b.

Parietes and basis not porose. Scutum and Tergum with very small articular ridges. Tergum broad, almost equilateral.

Hab.—Attached to a Gorgonia, Tubicoreen, near Madras, (Dr. Johnston). Hab. unknown, Mus. Cuming.

General Appearance.—I have seen only two specimens, kindly sent me by Dr. Johnston, and a single specimen in Mr. Cuming's collection. In most points this species agrees with the two last species. The shell (excepting the rostrum), and even the opercular valves in Mr. Cuming's specimen were of a very fine purplish-red; in the other specimens they were feebly tinted purple. The parietes are strongly ribbed internally, and are not permeated by pores. The basal cup is not porose, but its inner surface is ribbed in lines radiating from the centre, and in both these respects this species differs from the two foregoing. The Radii are rather narrow; they are paler coloured than the parietes; they have their sutural edges plainly crenated. The alæ have extremely oblique summits; the narrow rim added during the diametric growth of the shell is white, the rest of the sheath being, in Mr. Cuming's specimen, finely coloured like the parietes. Basal diameter of the longer axis of the largest specimen, .4 of an inch.

Scutum, rather narrow, with the basi-tergal corner much rounded off; externally the lines of growth are little prominent. Internally, the articular ridge is extremely little developed, and not at all reflexed; there is no adductor ridge; there is a minute pit for the lateral depressor muscle, placed almost on the edge of the valve. The Tergum is broad, forming (the spur being excepted) an almost equilateral triangle. The articular ridge is remarkably little prominent, and placed close to the scutal margin. The spur is nearly half as broad as the valve, with its extremity or basal margin in one case obliquely truncated, and in another case nearly square.

Animal's body unknown.

13. BALANUS NAVICULA. Pl. 3, fig. 6 a-6 d.

Parietes and basis not porose: carino-lateral compartments very narrow, and of nearly the same width from top to bottom: radii with their sutural edges smooth. Scutum externally striated longitudinally.

Hab.—Attached to Gorgoniæ, Tubicoreen, Madras (associated with B. calceolus), Dr. Johnston. Hab. unknown, Mus. Brit. and Darwin.

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This is a very distinct form, though nearer to the foregoing than to the other species. Its separation from the sub-genus Acasta is quite artificial; its affinity to this sub-genus is shown by its weaker shell, non-porose parietes and basis; by the radii having their sutural edges smooth, and their summits not quite square; by the carino-lateral compartments being very narrow; by the less elongated basis, not furrowed, from not clasping the branches of the Gorgonia; and by the longitudinally striated scuta; nevertheless, from the similar habits, and from the graduated structure in the five foregoing species, it cannot be removed out of the genus Balanus. I have seen three sets of specimens of this species.

General Appearance.—Shell, sometimes with the rostrum, and sometimes with the carina, and corresponding portions of the basal cup, elongated; but not, apparently, to so great a degree as in the foregoing species; basis not furrowed, from not clasping the branches of the Gorgonia. Colour pale blueish-purple, with the radii whiter. The surface is studded with small calcareous points. The carino-lateral compartments are very narrow, not more than one tenth of the width of the lateral compartments; they are, moreover, scarcely wider at the base than at the summit. The summits of the radii are, apparently, a little oblique, or at least not so square as in the foregoing species. The shell is not nearly so strong as in the last three species; and the compartments separate by gentle force, and from the action of caustic potash. The largest specimen was .4 of an inch in basal diameter.

Internally, the parietes are not very strongly ribbed, or they are almost smooth, and there are no pores. The basis is concave and smooth within, and is not porose. The sutural edges of the radii are quite smooth, or sometimes they exhibit, in the lower part, mere traces of septa,—a character by itself sufficient to separate this from the foregoing species. The alæ have oblique summits, and the rather narrow portion added during the diametric growth of the shell, is white.

The Scutum, externally (6 d), has raised striæ, radiating from the apex; valve rather thick; internally, the articular ridge is but slightly prominent, and its lower end is rounded off: the depression for the lateral depressor muscle is slight; between this depression and that for the adductor muscle, the surface of the valve is prominent. Tergum, somewhat beaked; externally, the surface is depressed in the line of the spur: the carino-basal margin slopes towards the spur.

Animal's body unknown.

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Section C.

Parietes and basis permeated by pores. Radii not permeated by pores.

———

14. BALANUS TRIGONUS. Pl. 3, fig. 7 a-7 f.

Parietes ribbed, mottled purplish-red; orifice broad, trigonal, hardly toothed. Scutum thick, with from one to six longitudinal rows of little pits. Tergum without a longitudinal furrow; spur truncated, fully one third of width of valve.

Hab.—Java; East-Indian Archipelago; Peru; West Columbia; California; Sidney; New Zealand. Mus. Brit., Cuming, Stutchbury, Dunker, &c.

General Appearance.—Shell conical, generally depressed; orifice broad, triangular, almost equilateral; walls coloured or only mottled with purplish-pink, having either irregularly branching, or regular, longitudinal ribs, which are generally white. The radii are pale pink, or nearly white: the opercular valves have either their upper parts, or nearly their whole surface, clouded with pinkish-purple: the epidermis is not persistent: the walls are moderately strong: the largest specimen was one inch, but generally full-grown specimens are about half an inch in basal diameter.

The Scuta have the lines of growth highly prominent. From one to five or six rows (7 b, 7 c) of nearly circular, or transversely oblong, deep pits, extend down the middle of the valve; rarely there is not even one row; in this latter case, the valve is not striated longitudinally. These little pits are caused by one or more deep longitudinal furrows, crossed by the lines, or rather ridges, of growth. In the same group of specimens, I have seen individuals with three, five, and six rows; and even a few specimens with only one row, or none at all. The outline of the valve is elongated, with the apex slightly reflexed: the inner surface is protuberant, sometimes to a remarkable, but variable degree. The articular ridge is not very prominent, but it extends fully half-way down the valve, and generally ends in a small free point. There is a short adductor ridge, and a deep narrow pit or cleft for the lateral-depressor muscle. Terga, externally smooth, flat, with scarcely a trace of a longitudinal furrow; spur broad (7 e, 7 f ), varying from half to one third of the width of

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the valve, with the end truncated, situated either near or quite close to the basi-scutal angle. The crests for the depressor muscles are moderately well developed.

Compartments.—The parietal tubes are, in their upper parts, filled up solidly, without transverse septa. The radii generally have their summits slightly oblique, and this is almost always the case with the radii of the rostrum; the other radii sometimes extend from tip to tip of the parietes, and are parallel to the basis; rarely the radii are considerably oblique. The septa of the radii are very obscurely denticulated, and the interspaces between them are filled up solidly. The alæ have their sutural edges thin and smooth.

Mouth.—Labrum with three teeth close together on each side of the central notch: mandibles with four teeth, the fourth being small, the fifth either absent or scarcely distinguishable from the inferior angle: maxillæ without any notch, with the two lower spines rather longer than the others. Cirri: in the first pair, one ramus is only half the length of the other; in the second pair, both rami are short and about equal in length; in the posterior pairs, the segments, which are not protuberant, bear four pairs of spines, of which the three lower pairs are short.

This species is widely-distributed, and where found seems to be common. It is generally attached to shells of mollusca, but I have seen it also attached to wood. I have found it associated with B. tintinnabulum, var. concinnus, and coccopoma, with B. psittacus, improvisus and amphitrite, and with Elminius modestus.

Young specimens bear a considerable resemblance to certain young varieties of B. tintinnabulum, and can indeed be distinguished from them only by a careful examination of the opercular valves; for it should be borne in mind, that in certain cases the scuta in B. tintinnabulum are pitted with little cavities. This species in some respects is, I think, allied to B. porcatus, but it is far more closely related to B. spongicola, and can be discriminated with difficulty from certain varieties of this latter species. In Mr. Cuming's collection, there is a group of small specimens, crowded between some older specimens, which are remarkable from the shell being oval in a transverse section,—from the smoothness of the walls,—and from the absence of pits on the scuta; yet there could be no doubt that these specimens belonged to our present species.

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15. BALANUS SPONGICOLA. Pl. 4, fig. 1 a-1 d.

BALANUS SPONGICOLA. Brown's Illustrations of the Conchology of Great Britain (1827), pl. 7, fig. 6: 2d edit. (1844), pl. 53, figs. 14-16.

Parietes generally smooth, sometimes longitudinally folded; coloured pink: orifice toothed. Scutum longitudinally striated. Tergum, with the apex produced, without a longitudinal furrow; spur truncated, about one third of width of valve.

Var. with the walls slightly folded longitudinally.

Hab.—South coast of England, and Tenby in South Wales, often imbedded in sponges; attached also to shells and rocks in deep water; Mus. Brit., Jeffreys. Algiers, on Mytili and Serpulæ, with B. perforatus, Mus. Mac Andrew. Madeira, with B. tulipiformis, Mus. Lowe. Lagulhas Bank, Cape of Good Hope, on detached kelp, with B. Capensis, Mus. Sir J. Ross. Imbedded in sponge with Acasta spongites, Mus. Bowerbank. Var. West Indies.

Fossil in Coralline Crag, Mus. S. Wood.

General Description.—Shell tubulo-conical; orifice of moderate size, rather deeply toothed; colour dull pink, or purplish, or dark flesh-colour; sometimes the radii are paler, sometimes of the same colour with the parietes. Surface smooth when well preserved, having transverse rows of minute spines. In the West Indian variety the walls are slightly or much folded, but I will describe this form separately. Size of largest specimen (Mus. Jeffreys), .6 of an inch in basal diameter.

Scutum, with fine ridges radiating from the apex, and with the lines of growth, crenated: internally, the articular ridge is small, adductor ridge short and barely distinct: there is a rather deep and narrow pit for the lateral depressor muscle. The whole valve is much thinner than in B. trigonus, which in most respects it closely resembles. Tergum, with the apex pinkish purple, produced or beaked, but the beak is not needle-like, as in B. psittacus and its allies, for the carinal margin is perfectly preserved up to the tip. Externally the valve is nearly flat, for the longitudinal furrow is very shallow. The spur is about one third of the width of the valve; its lower end is abruptly truncated: in European specimens (1 b) the whole basal margin, on the carinal side, slopes down to the spur in a straight line, which, together with the sharpness and production of the basi-scutal angle of the spur itself, gives to the whole valve a peculiar appearance: in the specimen (1 c) from the Lagulhas Bank, the basal margin on the carinal side is a little more hollowed out, but it is quite impossible to doubt about the specific identity of these specimens: in the West Indian variety (1 d) the basal

15                      

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margin on the carinal side forms a distinct but obtuse angle with the spur. In all cases the crests for the depressor muscles are very feebly developed.

The Compartments have their radii developed to a rather varying degree, with their summits oblique; hence the orifice is toothed: the sutural edges of the radii have their septa barely denticulated; the sutural edges of the alæ are smooth. The basis, as with the other species of this section, is permeated by pores; yet I found one specimen, from the Cape of Good Hope, with the basis apparently solid, thus offering a very singular anomaly. In the specimen imbedded in sponge, the basis, as viewed externally, is concave; whereas in Acasta, which always inhabits sponges, the basis is highly convex or hemispherical.

The Mouth and Cirri resemble those of B. trigonus, and I can point out no distinguishing character.

With respect to the variety from the West Indies, I have seen two sets of specimens differing somewhat in external appearance, one set attached to a coral from St. Vincent's, and another set to an Avicula from an unknown locality; at first I described these specimens, with some hesitation, as a distinct species, and I am very far from sure whether this would not have been the more correct course, although I am unable to point out any sufficient diagnostic characters. This form differs from the ordinary B. spongicola, in the walls being more rugged, stronger, and slightly or deeply folded longitudinally; in this latter case the shell in external aspect differs much from ordinary specimens of B. spongicola; but this is a variation so common that I dare not place any reliance on it. The colour is more purple; the summits of the radii perhaps rather less oblique. In the scuta the only difference is that the articular ridge seems rather longer, and the adductor ridge perhaps more prominent: in the terga, as already remarked, the basal margin on the carinal side does not slope so straight into the spur. These differences I consider all too slight to be of specific value. The difficulty in determining the nature of this variety is added to by its approach to B. trigonus in all those points in which it departs from the ordinary B. spongicola, so that for a short time I was even tempted to consider both these species as varieties of one form. But until B. trigonus is found with its scutum longitudinally striated, and with its tergum beaked, it can hardly be confounded with B. spongicola; for it should be observed that when in B. trigonus the rows of little pits disappear from the scuta, as sometimes happens, though rarely, yet these valves do not become longitudinally striated.

Balanus spongicola occurs, mingled with B. tulipiformis, in the Mediterranean, and by the external characters of the shell alone cannot be distinguished from that species; but the striated scuta and beaked terga suffice to separate them. Again, this species, at the Cape of Good Hope, occurs mingled with B. Capensis, and from the non-striped young varieties of that species, it can, externally, be distinguished only by the beak of the tergum not being sharp like a needle. I have seen a single, perfectly characterised specimen, with its opercular valves preserved, found by Mr. S. Wood in the Coralline Crag at Sutton, mingled with B. inclusus.

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16. BALANUS LÆVIS. Pl. 4, fig. 2-2 g.

BALANUS LÆVIS. Bruguière. Encyclop. Meth. (1789), Pl. 164, fig. 1.*

— DISCORS. Ranzani. Mem. di Storia Nat., 1820, Tab. 3, figs. 9 to 13.

— COQUIMBENSIS. G. B. Sowerby, in Darwin's Geology of South America (1846), Tab. 11, fig. 7.

Shell covered by brown membrane, or naked and white or pale purple; orifice small; radii very narrow. Scutum with one or two deep longitudinal furrows.

Var. nitidus (fig. 2): shell not covered by membrane, white or pale purple: orifice but slightly toothed: scutum generally with two furrows. Hab.—Chile, as far south as Concepcion; Peru; California.

Var. Coquimbensis (fig. 2 a): with the basal cup partly filled up with thin, irregular, calcareous layers, making a cancellated mass. Fossil, and recent.

Hab.—Strait of Magellan, ten to twenty fathoms, attached to shells; often entirely surrounding pebbles, forming globular masses; associated with Verruca lævigata. Chile and Peru, (generally var. nitidus), often attached to Balanus psittacus. California. Very common.

Fossil in an ancient tertiary formation (middle bed) at Coquimbo, Chile. In a recent deposit (var. nitidus) at the height of 1000 feet at Valparaiso; with Human remains at San Lorenzo, Callao, Peru.

I may premise that, having myself collected this species from the same locality, the Strait of Magellan, where no allied species occurs, attached to the same Mytilus and associated with the same Verruca, I feel confident that it is the B. lævis described by Bruguière; and there can hardly be any doubt that it is the B. discors of Ranzani. With respect to the old tertiary specimens from Coquimbo, named B. Coquimbensis by Sowerby, they differ from the recent in no respect, except in being considerably larger; and therefore I cannot consider them specifically distinct. At first I was unwilling to believe that the specimens with

* M. Deshayes, in his descriptions of the plates, considers this figure, I have no doubt erroneously, as that of B. perforatus, of Bruguière. The B. Coquimbensis of Sowerby, is a different species from the B. Coquimbensis, of Chenu, 'Illust. Conch.,' tab. 6, which latter is unknown to me.

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a single very broad longitudinal furrow, and those with two rather broad, or with one narrow furrow, on their scuta, could belong to the same species; but I soon found that all these varieties occurred mingled together, and that they differed in no other respect whatever. Generally, however, all the individuals in the same cluster had the same variety of scutum,—thus adding one more to the many instances amongst cirripedes of variations common to whole groups of specimens. Still more unwilling was I to believe that var. nitidus and the common variety could belong to the same species. Their general aspect is totally unlike: var. nitidus has a smooth, clean, naked shell, either white or pale purple, somewhat globulo-conical, often with a nearly entire orifice; whereas the other common variety generally has a more steeply conical shell, with a toothed orifice, and is covered by a dirty brownish membrane. Moreover, though I have seen hundreds of specimens from Tierra del Fuego, I have not seen one specimen of var. nitidus, or even of an approach to it in appearance; and, on the other hand, var. nitidus is the common form in Chile and Peru; though I have seen one or two specimens of the membrane-covered variety from Valparaiso. Such facts strongly induced me to believe that these forms were specifically distinct; but upon careful examination I could find no other or more important differences than those just specified. Some specimens from northern Chile are in an intermediate condition; and from Concepcion, in the south of Chile, where the climate approaches in character to that of the more southern parts of the Continent, there are many specimens, in so intermediate a condition that I know not whether or no to rank them under var. nitidus. Thus I became convinced that these forms are only varieties. At Concepcion, some few specimens are pale purple, and yet are wholly invested by thick brown membrane, thus uniting the two extreme varieties. From California I have seen both varieties, but I do not know which is most common there. With respect to the great difference in aspect between the specimens from northern Chile and Tierra del Fuego, we shall hereafter see a strictly analogous case in Balanus flosculus.

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Finally, I may add that B. lævis seems to represent in the southern hemisphere and on the west coast of North America, the B. perforatus of Europe and Western Africa.

General Appearance.—Shell conical, sometimes slightly globular; surface smooth (that is, not folded), either naked, and in that case white or pale purple, or covered by dirty yellowish-brown membrane. Orifice small, more or less toothed, rarely exceeding one third of the basal diameter. Radii very narrow, often not developed, the six sutures forming in all cases deep and narrow clefts. The largest recent, but much depressed, specimen which I have seen (from the Strait of Magellan) was three fourths of an inch in basal diameter; specimens growing congregated are often much elongated. I have seen one with the basal cup between two and three times as deep as the height of the compartments. Of the ancient tertiary specimens, the largest had a diameter of three fourths of an inch, and a total length of actually two inches (fig. 2 a); another of these fossils had a basal cup in depth equalling four fifths of the entire length of the shell and basis.

The scutum has either one very broad and deep longitudinal furrow (2 b), or two moderately broad and deep (2 e), or two narrow and deep, or less frequently one narrow and inconspicuous longitudinal furrow (2 f ); rarely there is not one furrow; sometimes there are none towards the apex, whilst furrows have been formed in the lower part of the valve. In young specimens the furrows extend down to the actual basal margin, but in old specimens they often fall short of this, and, as a consequence, the furrows become crossed by one, two, or three calcareous ridges, which ridges at successive periods formed the basal margin of the valve. The external surface is covered by yellow membrane; and fragments of several successive opercular membranes are often attached to the zones of growth.

Internally the articular ridge is not very prominent, but is remarkable (2 c, 2 d) from its lower point being produced into a long, sharp, sub-cylindrical, free style (like the hinge of a common gate), which is generally broken off in disarticulating the valve from the tergum. The adductor ridge is either sharp and prominent or blunt: it extends up the middle of the valve nearly to the apex, and downwards it trends a little towards the occludent margin. The pit for the lateral depressor muscle is minute but deep: the basal margin is sometimes hollowed out under this pit. Sometimes there is a distinct, but blunt ridge, caused by one of the furrows outside, parallel to the adductor ridge, and placed between it and the little pit for the lateral depressor; in this case, the basal margin, as viewed internally, is rendered sinuous (2 d), as is best exhibited in the great fossil specimens from Coquimbo.

Tergum (2 g).—Spur of moderate length and breadth, with its lower end obliquely truncated and rounded. The longitudinal furrow has its edges somewhat folded in. The basal margin on the carinal side of the spur is sometimes a little hollowed out. The crests for the depressor muscles are well developed; but the corner of the valve supporting them is extremely thin, and is often imperfectly calcified.

Compartments.—The parietal tubes are not crossed by transverse

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septa, but in their upper parts are filled up solidly. The radii are always very narrow, with their summits oblique, though to a variable degree: their sutural edges have fine and closely approximate septa, with minute denticuli: the sutural edges are received in a furrow, on the opposed compartment, of unusual depth; hence the lines of suture run, in the lower part of the shell, almost exactly in the middle between each two compartments. The alæ are added to above the level of the opercular membrane.

The Basis is often thick, with an underlying layer, largely cancellated or honeycombed. When many specimens grow crowded together, the basis is generally deeply cup-formed, or even sub-cylindrical; and equals as much as four fifths of the length of the entire shell. In such cases, in some few recent specimens, and in all the large or even quarter-grown old tertiary specimens, but not in the quite young fossil specimens, a structure is presented, which I have not seen in any other Cirripede, namely, the basis (Pl. 4, fig. 2 a) is filled up for one third, or even for more than half its depth, by successive, separate, calcareous, transverse layers or septa. It would appear as if the basal cup had grown too large for the animal's body, and so required filling up. The layers are thin and fragile; a single layer never stretches across the whole shell; each is irregularly mammillated or blistered, with the convex surfaces generally directed upwards; the layers are furnished on their under sides with little pillars and short ridges, resting on the layers beneath; it rarely happens that the supports of one layer lie directly over those of another, though this is sometimes the case. In a vertical section, the mass formed by these irregular layers has a coarsely cancellated structure. This structure, although confined to this one Cirripede, is not so anomalous as might at first be thought, for in most species of the genus, each time that the circumference of the basis is added to, an excessively thin calcified film is thrown down over its whole inner surface; and in any of these species, if the films had been formed thicker and had rested only on certain points, instead of over the whole underlying layer, the cancellated structure above described would have been produced.

Mouth: the labrum is either destitute of teeth, or has two or three very minute teeth. The palpi have a tuft of very long spines at their ends. The third tooth of the mandibles is thicker and larger than the two upper ones. The maxillæ have either a nearly straight edge, or the inferior corner is obliquely truncated, and projects much beyond the rest of the edge. In the Cirri, none of the segments are very protuberant: in the first pair, one ramus is nearly twice as long as the other: in the posterior pairs, the segments are not much elongated, but each supports seven pairs of spines.

Var. nitidus: with respect to this variety I have little to add to my preliminary remarks on its peculiar appearance, owing to its smooth, naked condition, and pure white or pale purple colour. This colour, when examined through a lens, is seen to consist of very fine longitudinal stripes; and is produced by the calcareous matter within the longitudinal parietal pores being thus coloured. Generally the scuta have two longitudinal furrows; but I have seen a scutum of one perfectly characterised specimen with only a single broad furrow, like that

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which frequently occurs in the membrane-covered variety. Var. Coquimbensis, as before stated, differs only in its greater size: the scutum, in the one specimen examined, had two broad longitudinal furrows; neither it, nor the tergum differed from certain varieties now found on the coast of Chile.

17. BALANUS PERFORATUS. Pl. 5, fig. 1 a-1 d; Pl. 4, fig. 3 a-3 c.

BALANUS PERFORATUS. Bruguière. Encyclop. Meth., 1789, Tab. 164, fig. 12 infra.

LEPAS ANGUSTA. Gmelin. Syst. Naturæ, 1789.

— ORE ANGUSTIORE. Chemnitz. Vol. viii, Tab. 98, fig. 835.

BALANUS CORNUBIENSIS CONICO ORE MINORE. Ellis. Phil. Trans. vol. 50, 1758, Tab. 34, fig. 16.

LEPAS BALANUS ET FISTULOSUS. Poli. Test. Siciliæ (1795), Tab. 4, fig. 5, Tab. 6, fig. 1.

BALANUS COMMUNIS. Pulteney. Dorset Catalogue, 1799.

— — Montagu. Test. Brit., 1803.

LEPAS ANGUSTATA. Wood. General Conchology, 1815, Pl. 6, fig. 5.

BALANUS CRANCHII. Leach (!). (B. Blainvillii in Tab.) Encyclop. Brit. Suppl., vol iii, 1824.

— — Brown. Illust. Conch., 1827, Pl. 7, fig. 9, 10, and 2d Edit., Pl. 53, fig. 9-12.

— PERFORATUS. Chenu. Illust. Conch., Tab. 3, fig. 9, Tab. 6, fig. 15.*

Shell pale purple, or white, or dirty ash-colour; smooth, or, from being corroded, finely ribbed longitudinally; sheath purple; orifice generally small; radii generally narrow or absent. Scutum, internally, with a short minute ridge, parallel and close under the prominent adductor ridge. Tergum with the apex somewhat produced.

* I have very little doubt regarding any of these references: I have no means of ascertaining the priority, within the same year, of Gmelin and Bruguière, but have given it to the latter, as perforatus is much the best known specific name. English conchologists seem generally to suppose that the B. communis of Pulteney and Montagu is the B. porcatus of this work; but I have not the smallest doubt that I have given it rightly as a synonym of the present species; the indistinctness of the compartments, the multitude of fine ridges, the smallness of the orifice, the longitudinal furrow on the terga, the colour, size, and habitat, all given by Pulteney or Montagu, will agree with no other British species. The Lepas balanus of Poli, which is certainly a synonym of our present species, has been erroneously considered by several authors to be the same with the L. balanoides of Poli, which latter undoubtedly is the B. amphitrite of this work.

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Var. angustus (Gmelin) Pl. 5, fig. 1 a: pale dull purple or white; orifice small or of moderate size; radii very narrow or moderately wide, white or pale purple, with oblique summits.

Var. Cranchii (Leach) Pl. 5, fig. 1 b: corroded, covered with fine longitudinal ridges owing to the exposed, filled-up, parietal tubes; dark dirty ash-colour, with a tinge of purple: radii not developed, or very narrow with oblique summits; orifice small.

Var. fistulosus (Poli) Pl. 5, fig. 1 d: shell cylindrical, white or dull purple; orifice of moderate size or small; basis deeply cup-formed.

Var. mirabilis, Pl. 5, fig. 1 c: bright purple; radii white, very broad, with their summits parallel to the basis; orifice entire, large.

Hab.—Southern shores of England; South Wales; Mediterranean; Western Africa, southward to Loanda, in 9° S.; West Indies (?). Generally adhering to rocks at a low tidal level; in one case attached to the floating Lepas Hillii, Mus. Jeffreys.

This is a well-marked species, and in its essential characters does not vary much; but owing to the shell being almost as often white as purple,—to its being remarkably subject to disintegration,—to its often becoming cylindrical,—to the radii being either not at all, or slightly, or moderately, or largely developed, and consequently to the orifice of the shell varying in size, the general external appearance of the different varieties is singularly diversified; but when a series of specimens is examined, it is easy to see how one form passes into another.

General Appearance.—Shell conical, with the orifice oval, unusually small, being generally only from one third to half of the basal diameter; sometimes moderately large; in one single instance as wide as the basis. Radii, often represented by mere lineal fissures, or they are narrow, or sometimes moderately wide. Colour pale, dull purple, sometimes lilac, often passing into a dead pure white: the same individual will occasionally have one part of its shell white, and another purple: the purple tint almost invariably is nearly uniform, or not in stripes. The radii are generally white, when the whole shell is purple, but sometimes they are pale purple: the sheath is apparently always coloured of a fine claret-purple, with the triangular portion of the alæ, added during diametric growth, generally white, but sometimes purple. The surface is quite smooth, but very often, especially on the shores of England, whole groups of specimens (excepting the very young ones,) have had the outer lamina of the parietes entirely corroded and removed; in this case the shell assumes a dirty, more or less dark, ash-colour, feebly tinted with purple, and the whole surface, owing to the exposure of the solidly filled-up parietal tubes, becomes finely striated, or covered with very narrow, longitudinal ridges. When specimens are crowded together they often become cylindrical, and

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much elongated, owing to the basis becoming deeply cup-formed: I have seen specimens, half an inch in diameter in the widest part, one inch and a half in height, the walls forming only a third of this. The largest specimen which I have seen (from the southern shores of England) had a basal diameter of 1.2 of an inch; some very steeply conical specimens were .9 of an inch in height, and .8 in basal diameter.

Scuta, externally, slightly convex; growth-ridges approximate, moderately prominent. Internally (Pl. 4, fig. 3 a) the articular ridge is moderately developed, with the lower end produced downwards into a freely depending, flattened style, somewhat variable in size, but not so long as in B. lævis, and easily broken in disarticulating the valves. The adductor ridge is very prominent, running from almost the apex of the valve, close to the articular ridge, to near the basal margin. The basi-tergal portion of the valve is converted by the adductor ridge into a rather deep cavity, within which there is a short, sharp, and minute ridge, close and parallel to the adductor ridge, and bounding the impression left by the lateral depressor muscle: this insignificant ridge was present in every specimen; it occurs only in very few other species, as in B. nubibus and cariosus. The thickness of the valve sometimes varies a little, and when thick the adductor ridge does not appear quite so prominent. Tergum, with the apex moderately beaked and produced; beak triangular in section, coloured dark purple, as is the upper internal surface of the valve; the longitudinal furrow is deep, and has its edges folded in, and even quite closed. The spur is moderately long and narrow; but its width varies a little (Pl. 4, fig. 3 b, 3 c), and consequently it stands at either rather above or at twice its own breadth from the basi-scutal angle: its lower end is either bluntly pointed or square, and generally is feebly toothed on the under-side. The basal margin of the valve generally slopes a little, on both sides, towards the spur. Internally, the scutal margin is but slightly inflected: the articular ridge is but slightly prominent, and but little curved; in the upper part of the valve there are generally several very minute ridges, parallel to the articular ridge, on the side towards the scutum. The internal surface of the spur itself is sometimes concave. The crests for the carinal depressor muscle are barely developed. It may here be mentioned that on the opercular membrane many long spines stand rudely arranged in rows.

Parietes: the parietal tubes have not transverse septa; but are solidly filled up in their upper parts by dark-purple layers of shell. The radii, as already stated, are either not at all developed, or are extremely or only moderately narrow, with their summits more or less oblique: in Mr. Cuming's collection, however, there is an unique specimen, var. mirabilis (Pl. 5, fig. 1 c) with the aperture of the shell as wide as the basis, with bright purple parietes, and white, very broad radii, having their summits parallel to the basis. The septa of the radii are finely denticulated, and the interspaces are filled up solidly. The alæ have very oblique summits, and their edges are finely crenated. Basis, flat, or deeply cup-shaped; there is often an underlying, coarsely-cancellated layer.

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Mouth: labrum finely hairy, but without any teeth; mandibles, with the 4th tooth small; the 5th confluent, with the sometimes smooth, sometimes pectinated inferior angle. Maxillæ, rather broad, with a slight notch under the upper pair of spines. Cirri, first pair, with one ramus, having 29 segments, and above one third longer than the shorter ramus, having 17 segments; these latter segments are remarkable by the extent to which their upper front surfaces are laterally produced into projections, twice as long as the breadth of that portion of the segment which is articulated to the adjoining segment. These projections have a double row of serrated spines on their upper edge, and a beautiful radiating bundle at the end; the projections decrease in length, both in the upper and lower segments. The second cirrus (Pl. 29, fig. 4) has the segments (13 in number, in the same individual with the segments above enumerated) of both rami produced in the same singular manner as in the first pair. The third pair have only inverted conical segments, coloured darker purple than the other cirri. The sixth pair had in the same individual 31 or 32 segments, and therefore one or two more than in the longer ramus of the first pair.* The segments in the posterior cirri have their anterior faces shield-shaped, and bear 6 or 7 pairs of spines, with some minute intermediate spines. There is the usual point at the dorsal basis of the penis.

Range.—This species is common on the southern shores of England and in the Channel Islands: the largest specimens which I have seen came from these quarters. The most northern point whence I have seen specimens, is Tenby, in South Wales. This species is common throughout the Mediterranean; I have seen specimens from Malaga, Sicily, Algiers, and Smyrna; thence it ranges down the western coast of Africa, as far south as the Gambia and Loanda, in 9° south latitude. I believe British specimens are more often corroded than those from further south. Amongst some old, ill-kept specimens in a box in the British Museum, marked "Kingston, Jamaica," there were some of this species: also I received some specimens, marked "S. America," from Mr. G. B. Sowerby: again, Ellis, in Phil. Trans., vol. 50, part 11, gives a figure (Tab. 34, fig. 15) of some specimens from the West Indies, which I believe to be B. perforatus: hence, it is in some degree probable that this species, like B. tintinnabulum, and amphitrite, and improvisus, may be found on both sides of the equatorial Atlantic. Balanus perforatus is attached, together with B. tulipiformis, trigonus, amphitrite, Chthamalus stellatus, and Pollicipes cornucopia, usually to rocks, near the lower limit of the tidal level; but I believe, from specimens kindly sent me by Mr. Mac Andrew, that it is frequently obtained by dredging; one specimen was even marked 30 fathoms. According to Poli, it is sometimes attached to the bottoms of vessels; and I have seen a specimen adhering to the floating Lepas Hillii.

Affinities.—This is a distinct species, closely allied to no other species, but comes nearest to B. lævis, which is its representative in

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* Under the Genus (p. 190) I have given the numbers of the segments in the cirri of this species at successive ages.

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Southern America, and on the whole west coast of that continent. It is allied to that species, and differs from most other species, in the general form of the shell, its small orifice, narrow radii, and often deeply cup-formed basis. It agrees to a certain extent in the colouring, though the purple here is much more prevalent, and is not confined to the shelly matter filling up the parietal tubes. It agrees with that species in the general structure of the scutum; but the two or three deep, longitudinal furrows are here absent; and the minute ridge, parallel to and almost under the adductor ridge, is a peculiarity confined to this and very few species in the genus. The terga differ from those of B. lævis, chiefly in the spur being narrower, and in the apex being beaked. Lastly, the highly protuberant segments of the one ramus in the first cirrus, and of both rami in the second pair, are here remarkable. With regard to the varieties, I have nothing to add to their short diagnostic characters above given.

18. BALANUS CONCAVUS. Pl. 4, fig. 4 a-4 e.

BALANUS CONCAVUS. Bronn. Italiens Tertiar-Gebilde (1831) et Lethæa Geognostica, b. ii, s. 1155 (1838), Tab. 36, fig. 12.*

— CYLINDRACEUS, var. C. Lamarck. Animaux sans Vertebres (1818).

LEPAS TINTINNABULUM. Brocchi. Conchologia Sub-Appen., t. ii, p. 597 (1814).

Shell longitudinally striped with white and pink; or dull purple; sometimes wholly white. Scutum finely striated longitudinally; internally, adductor ridge very or moderately prominent.

Hab.—Panama; Peru; S. Pedro in California; Philippine Archipelago; Australia. Mus. Brit., Cuming, Stutchbury, Aug. Gould.

Fossil in Coralline Crag, England; Mus. Brit., S. Wood, Bowerbank, Lyell, J. de C. Sowerby, Tennant. Sub-Appennine formations, near Turin, Asti, Colle in Tuscany, Mus. Greenough, &c. Tertiary beds, near Lisbon, Mus. D. Sharpe and Smith. Bordeaux (?) Mus. Lyell. Tertiary beds, Williamsburg; and Evergreen, Virginia, Mus. Lyell. Maryland, Mus. Krantz. Recent formations† near Callao, Peru, Mus. Darwin.

This species has caused me much trouble. Looking first to the recent specimens, I examined several from Panama

* I suspect that B. pustularis, miser, and zonarius, all figured by Münster, in his 'Beiträge,' b. iii, Tab. 6, may be this species.

† I procured this specimen from the Island of S. Lorenzo, off Callao; it was imbedded, together with seventeen species of recent shells and with human remains, at the height of eighty-five feet.

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and California, which, though differing greatly in colour, resembled each other in their scuta having the adductor ridge extremely prominent, and in having (Pl. 4, fig. 4 a,) an almost tubular cavity for the attachment of the lateral depressor muscle,—characters which at first appeared of high specific value; but I soon found other specimens from Panama in which these peculiarities were barely developed. I then examined a single specimen from the Philippine Archipelago, resembling in external appearance one of the Panama varieties, but differing in the scuta being externally strongly denticulated in lines instead of being merely striated,—in the adductor ridge being far less prominent,—and in the spur of the tergum being broader and more truncated; I therefore considered this as a distinct species. I then examined a single white rugged specimen from the coast of Peru, which differed from the Philippine specimen in the shape of the well-defined denticulations on the scuta, and in some other trifling respects, and in the segments of the posterior cirri bearing a greater number of spines; with considerable doubt, I also named this as distinct. But when I came to examine a large series of fossil specimens from the Coralline Crag of England, from northern Italy, from Portugal, and from the southern United States, I at once discovered that the form of the denticuli on the scuta was a quite worthless character,—that in young specimens the scuta were only striated,—that the prominence of the adductor scutorum ridge and the depth of the cavity for the lateral depressor muscle varied much (as in the case of the recent specimens), owing apparently to the varying thickness of the valve,—that in the terga the spur varied considerably in length and breadth, the latter character being in part determined by the varying extent to which the edges of the longitudinal furrow are folded in,—and lastly, that in young specimens the basal end of the spur is much more abruptly truncated than in the old. Hence I have been compelled to throw all these forms, originally considered by me as specifically distinct, into one species. I must repeat that this considerable variation in the prominence of the adductor ridge, and in the depth of the pit for the lateral depressor muscle—the pit in some cases becoming even tubular—is a very unusual circumstance.

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With respect to the fossil specimens* from the above-stated several distant localities, I consider them as certainly belonging to one species, though varying considerably in several points of structure. When compared with the recent specimens, they differ from them in often attaining a considerably larger size; in the parietes being often, but not always, longitudinally ribbed; and in the radii often having more oblique summits. On the other hand, considering the many points of identity between the fossil and the recent specimen, I have concluded, without much doubt, that they ought all to be classed together. I may remark that, in the Coralline Crag specimens, the spur of the tergum (Pl. 4, fig. 4 d,) is unusually long and narrow; it is broader and shorter in the Italian specimens (4 e), and variable in this respect, in the United States specimens; the scuta of the Lisbon specimens are remarkable for the greater prominence of the adductor ridge, and for the depth of the lateral depressor cavity. Some of the specimens from all the several localities are identical with the recent ones from the coast of Peru. The walls of the shell in the Coralline Crag specimens, are generally ribbed longitudinally. I have entered into the above particulars, on account of, in the first place, its offering an excellent example how hopeless it is in most cases to make out the species of this difficult genus without a large series of specimens; secondly, as showing how the characters alter with age; and thirdly, as a good instance of the amount of variation which seems especially to occur in most of the species which have very extensive ranges.

Some of the pink-striped Panama varieties, though having a somewhat different aspect, can be distinguished from certain varieties of B. amphitrite only by their scuta being longitudinally striated,—a character in this species variable in degree, and in most cases of very little value. Some of the other recent varieties are sufficiently distinct from B. amphitrite; and the great fossil Coralline Crag specimens, which stand at the opposite end of the series of varieties, with their ribbed walls, very oblique radii, and coarsely striated scuta, are extremely unlike B. amphitrite. With respect to the no-

* These will be fully illustrated in the monograph on the Fossil Balanidæ, to be published by the Palæontographical Society.

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menclature of the present species, I have little doubt that I have properly identified the Italian fossil specimens with B. concavus of Bronn, who has given a very good figure of this species in his 'Lethæa Geognostica;' it must, however, be confessed that the longitudinal striæ on the scuta are not there represented. Considering the large size and frequency of this species in Europe and in the United States, it has probably received several other names, besides the two incorrect synonyms, quoted at the head of this description. I should add that the true B. cylindraceus (not var. C) of Lamarck, according to the plate given by Chenu in his 'Illust. Conch.,' is the B. psittacus of South America. I have seen in collections specimens of B. concavus labelled as B. tulipa of Poli (B. tulipiformis of this work),—a very natural mistake, without the opercular valves be carefully examined.

General Appearance.—Shell conical, often steeply conical; orifice rather small, with the radii narrow, and generally in the fossil specimens very oblique; surface generally smooth, sometimes rugged, and in the coralline crag specimens generally ribbed longitudinally, the ribs being narrow. Colour various, either dull reddish-purple with narrow nearly white, or wider dark longitudinal bands; or, again, pale rosy-pink with broad white bands; or lastly, wholly white. The radii are either darker or paler than the parietes. The opercular valves are either dark purple or nearly white. Pale pink and white stripes are visible on some of the Italian and Portuguese tertiary specimens; and in most of the fossils the sheath is tinged dull red.

Dimensions.—The largest actually recent specimen which I have seen, from the Philippine Archipelago, had a basal diameter of 1.2 of an inch; the Peruvian pleistocene specimen is 1.7 in diameter; specimens from the crag and from the Italian deposits, however, sometimes slightly exceed two inches in basal diameter, and three in height.

Scuta: these in young and moderately-sized specimens are striated, sometimes very faintly, but generally plainly, causing the lines of growth to be beaded; but often, in large and half-grown specimens, the lines of growth are extremely prominent, and being intersected by the radiating striæ, are converted into little teeth. As the striæ often run in pairs, the little teeth frequently stand in pairs, or broader teeth have a little notch on their summits, bearing a minute tuft of spines. In very old and large specimens, the prominent lines of growth are generally simply intersected by deep and narrow radiating striæ. In one case, a single zone of growth in one valve was quite smooth, whilst the zones above and below were denticulated. The valve varies in thickness, which I think influences the prominence of the lines of growth and the depth of the striæ. These striæ often affect the internal surface of the basal margin, making it bluntly toothed. The articular ridge is rather

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small, and moderately reflexed: the adductor ridge (as already stated,) varies remarkably; in most of the Panama specimens, it is extremely prominent, and extends down to near the basal margin; in other specimens it is but slightly prominent, especially in some of the fossil specimens from Virginia. The cavity for the lateral depressor, also, varies greatly; it is often bounded on the side towards the occludent margin by a very slight straight ridge, which occasionally folds a little over, making almost a tube; this, at first, I thought an excellent specific character, but far from this being the case, the cavity often becomes wide, quite open, and shallow.

Terga, very slightly beaked; the surface towards the carinal end of the valve, in some of the fossil specimens, is very slightly striated longitudinally. There is either a slight depression, or more commonly a deep longitudinal furrow, with the edges folded in and touching each other, extending down the valve to the spur, and causing the latter to vary in width relatively to its length. When the furrow is closed in, the spur is about one fourth of the entire width of the valve, and has its lower end obliquely rounded, and stands at about its own width from the basi-scutal angle: when there is only a slight depression and no furrow (as is always the case with young specimens), the spur is broader, equalling one third of the width of the valve, with its lower end almost truncated, and standing at about half its own width from the basi-scutal angle. But the absolute length of the spur, also, varies considerably; it is often very long, compared to the whole valve. The basal margin on the carinal side is sometimes slightly hollowed out; when the furrow is closed, this latter side slopes towards the spur. Internally, the articular ridge and crests for the tergal depressor muscle are moderately prominent.

Parietes, the longitudinal septa sometimes stand near each other, making the parietal pores small. The radii have oblique summits, but to a variable degree; their septa are unusually fine, and are denticulated on their lower sides; the interspaces are filled up solidly. The alæ have their summits very oblique, with their sutural edges nearly or quite smooth. In most of the fossil specimens, and slightly in some of the recent specimens, the surface of the sheath presents an unusual character, in a narrow, longitudinal, slightly raised border, running along the sutures, on the carinal side of each compartment.

Basis thin, porose; sometimes with an underlaying cancellated layer.

Mouth: labrum with six teeth: mandibles with the fourth and fifth teeth small, either sharp, or blunt: maxillæ with a straight edge, or with the inferior part slightly prominent. Cirri with the rami of the first pair unequal by four or five segments: the segments in the shorter ramus are extremely protuberant. The segments in the second cirrus only moderately protuberant: but all the specimens were in bad condition, and it appeared as if, in the Panama specimens, the segments of the second cirrus were more protuberant than in the Philippine Island specimens. In the posterior cirri there are from three to five pairs of spines on each segment: even amongst the Panama specimens some had three and some four pairs, and a white Panama specimen had five pairs of spines.

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All the recent specimens which I have seen, were, with one exception, attached to various shells and crabs, and to each other. The Peruvian specimen was associated with B. flosculus. The tertiary specimens are often congregated together into great masses. Including the recent and fossil specimens, this species encircles the globe. During the miocene period it seems to have been the commonest existing sessile cirripede; now, it does not appear to be common, excepting, perhaps, at Panama: Mr. Cuming procured only one specimen from the Philippine archipelago.

19. BALANUS AMPHITRITE. Pl. 5, fig. 2 a-2 o.

LEPAS RADIATA. Wood's General Conchology (1815), Pl. 7, fig. 7.

— MINOR ? Wood's General Conchology (1815), Pl. 7, fig. 6.

— BALANOIDES. Poli. Testacea utriusque Siciliæ (1795), Tab. 5.

BALANUS BALANOIDES. Risso. Hist. Nat. de l'Europe Merid., tom. iv, 1826.

Shell longitudinally striped with purple or pink; sometimes with the stripes confluent; sometimes wholly white. Scutum internally with a prominent broad adductor ridge.

Var. (1) communis: (2 e, 2 h, 2 l,) nearly white, with pale or dark violet-coloured longitudinal stripes: epidermis rarely persistent: shell either thin or thick: radii white or freckled with reddish mahogany colour, with their summits either oblique, sometimes in a high degree, or nearly parallel to the basis: basal point of spur of the tergum either square or bluntly pointed. Hab. Mediterranean, W. Indies, S. Africa, Philippine Archipelago, New South Wales.

Var. (2) venustus: (2 a,) white or pale pink, with narrow bright pink, or broad pinkish-purple stripes; orifice either much dentated or nearly entire. Tergum with the carinal half of the basal margin sometimes much hollowed out. Hab. W. and S. Africa, Ceylon.

Var. (3.) pallidus: (2 c, 2 k,) white, with or without a yellowish persistent epidermis; sometimes with the edges of the compartments tinted purple: radii moderately oblique: tergum generally narrow, with the spur sharp, and the basal margin on its carinal side much hollowed out. Hab. W. Africa, Madagascar, Red Sea.

Var. (4) niveus: (2 f, ) white, with longitudinal hyaline lines; epidermis not persistent. Hab. W. Indies, Florida, S. Africa, &c.

Var. (5) modestus: upper part of shell white, lower part uniform blueish-grey, opercular valves as in Var. (1). Hab. unknown.

Var. (6) Stutsburi: (2 d, 2 i, 2 m, 2 n, 2 o,) white, with or without pinkish-purple stripes, which are often confluent, rendering the lower part of

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the shell of a uniform purplish tint; epidermis persistent: radii very narrow: tergum narrow, spur sharp, varying in form and in exact position; carinal margin sometimes highly protuberant; basal margin on the carinal side of the spur generally, but not invariably, much hollowed out. Hab. West Africa.

Var. (7) obscurus: (Pl. 5, fig. 2 g) with narrow, approximate, obscure and often almost confluent, slaty, or pale purplish-brown, or dark slate-coloured stripes. Hab. West Indies, Australia, and unknown.

Var. (8) variegatus: with narrow, approximate, dusky, claret-coloured stripes, transversely freckled with white; shell conical; walls very thin: scutum with the adductor ridge small. Hab. New Zealand.

Var. (9) (an. spec. ?) cirratus: (fig. 2 b) shell very pale purplish-brown, with faint, more or less plain longitudinal stripes, transversely freckled with white; walls thin: scuta with the lines of growth beaded: basis, in specimens growing in groups, irregularly cup-formed: maxillæ with the inferior corner extremely prominent. Hab. Mouth of Indus, Australia, Philippine Archipelago.

Hab.—Warmer temperate and tropical seas; extremely common; Mediterranean, Smyrna, Sicily, Coast of Portugal, West Coast of Africa, River Gambia, West Indies, Demerara, Natal, Madagascar, Red Sea, Mouth of the Indus, Ceylon, Philippine Archipelago, East Indian Archipelago, Pacific Ocean, east coast of Australia, New Zealand; extremely common on ships' bottoms; often attached to floating timber, canes, &c.; often associated with B. tintinnabulum; attached to pebbles and various shells.

With respect to the nomenclature of this extremely common species, which is widely distributed in all the warmer seas (excepting, as far as I have seen, on the west coast of America), there is some difficulty. I have no doubt that it is the Lepas radiata of Wood (1815), but Bruguière, in 1789, gave this same name to a Balanus which he had not seen, but which is figured in Chemnitz, Tab. 59, fig. 842. I should have thought that this also had been the present species, but Spengler, in describing (Skrifter af Naturhist. Selskabet i, B. 1790) this individual specimen, which he calls L. purpurea, states that it is 13 lines in basal diameter; now this is a size which is never acquired by B. amphitrite; and the description, habits, and size, would apply equally well to the species which I have called B. amaryllis; but when no notice is taken of such points of importance, as whether the walls are permeated by pores, whether the radii are smooth-edged, whether the scuta are striated, it is impossible to identify with any approach to certainty sessile Cirripedes; and the

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names given ought, in my opinion, to carry little weight with them. With respect to Lamarck's Balanus radiatus (1818), the synonyms quoted exhibit some great and inextricable confusion. The B. radiatus, again, of Risso, is a fossil and apparently distinct species. There can be no doubt that the present species is the Lepas balanoides of Poli, (and of several authors who have followed him), and equally little doubt that the present species is not the true L. balanoides of Linnæus, which has a membranous basis, and which I have not seen from the Mediterranean. Under these circumstances I have concluded that less confusion would be caused by giving a new name to this species than by taking that of Wood, which ought not to have been used by him, considering Bruguière's previous adoption of it.

Under the head of B. tintinnabulum I have alluded to the great variation of B. amphitrite, which consists not only in a vast diversity in the colouring and in the general aspect, but likewise in the degree of obliquity of the summits of the radii, in the form of the terga, and slightly in that of the scuta. In order to show that it has not been from indolence that I have put so many forms together, I may state that I had already named and fully described in detail eight of the following forms as species, when I became finally convinced that they were only varieties: it would require at least thirty figures, which I have not the power to give, fully to illustrate the transitional forms. As with B. tintinnabulum, the deception is wonderfully enhanced by whole groups of specimens from the same locality exactly resembling each other, and sometimes differing from other groups attached to the very same object. If a person were to get together only some fifty or sixty specimens from only half a dozen different localities, he would almost certainly come to the same conclusion, as I at first did, that several of the varieties are true species; but when he gets several hundred specimens from all quarters of the globe, he will find, to his trouble and vexation, that character after character fails and blends away by insensible degrees, and he will be led, as the more prudent course, to include, as I have done, and I hope rightly, all under one specific name. I have experienced

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more doubt regarding the last variety, cirratus, than on any other, on account of its peculiar colouring, and from the basis being often irregularly cup-formed. Under B. concavus I have remarked how closely some of its varieties approach to B. amphitrite, and it is to this last variety that they approach; almost the only difference being that the scuta in B. concavus are longitudinally striated. Yet some of the varieties of the two species are so distinct that it would be puerile to class them together. I will only add, that after studying such varying forms as B. tintinnabulum and amphitrite it is difficult to avoid, in utter despair, doubting whether there be such a thing as a distinct species, or at least more than half a dozen distinct species, in the whole genus Balanus.

As with B. tintinnabulum, I will first give a full description of the more common forms, alluding only to each less frequent variation, and then separately describe briefly the more marked varieties.

General Appearance.—Shape conical, either steep or considerably depressed; sometimes tubular; orifice either nearly entire or deeply toothed, not large, varying from rhomboidal to rounded-trigonal. Surface of shell smooth, never ribbed, generally naked, but occasionally the yellowish epidermis is persistent; in the same individual, I have seen all the lower part of the shell thus covered and the upper part naked, the line of separation being defined. The colour varies much, even sometimes considerably on the same individual; generally white or pale gray, with dull violet-coloured, longitudinal, moderately broad stripes; these stripes are sometimes equidistant, but more usually they are arranged so as to leave broad white spaces; the stripes fade away by endless variations, the edges of the compartments and the carinal end of the shell longest retaining any colour, until we have a uniformly white shell, generally covered with a yellowish epidermis; or the white is longitudinally marked with hyaline lines; this latter variety has a very peculiar aspect, and I did not doubt it was specifically distinct, until, in a number of specimens on a ship from the West Indies, I got the most perfect series, and another scarcely less perfect series from the Mediterranean, graduating into common coloured varieties. Rarely the dull violet or purple stripes become approximate and dark, so that the whole shell is tinted of a brownish slate-colour, occasionally freckled with white. Again, we have another set of very pretty varieties, with a white or very pale pink ground, with either narrow bright pink or broad pinkish-purple stripes. Again, I have seen numerous specimens of a variety, var. Stutsburi, from the west coast of Africa, in which the upper part of the shell is white, and the lower part shaded with

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pinkish or dark purple approximate stripes, which often become confluent; in one group, the whole shell being thus uniformly coloured, without any vestige of stripes. I have seen another group from an unknown locality, in which the lower part of the shell was uniformly blueish-grey. A variety from Australia has narrow approximate dark claret-coloured stripes, transversely freckled with white. Lastly, in the variety cirratus, the whole shell is very pale purplish-brown, with indistinct longitudinal brownish stripes, transversely freckled with white lines. I considered this as a distinct species, until quite lately finding forms which I could not possibly determine whether to class as B. cirratus or amphitrite.

The radii are generally snow-white, or freckled with a bright mahogany tint, or rarely clouded with purple, or in the pink varieties with pink. The scuta are dull purple or pink, generally with a white band along their tergal margin; often, however, they are white, with merely one or two purple fasciæ. The thickness or strength of the shells varies much; some specimens attached to a floating cane, from Natal and the Philippine Archipelago, were extremely strong; others, from the Mediterranean and Australia, and some tubular varieties from the West Indies, were very thin, translucent, and fragile. Size: large specimens generally attain a diameter of from half to three quarters of an inch in basal diameter; and I have seen one or two specimens an inch in diameter.

Scutum; sometimes the surface is very smooth, but generally the growth-ridges are moderately prominent; the latter are occasionally very finely beaded, and this seems always the case with var. cirratus. Internally, the articular ridge is prominent and reflexed: the adductor ridge is sharp, very prominent, and straight; it runs parallel to the occludent margin; close to its lower side there is often a depression (Pl. 5, fig. 2 i), sometimes bounded by a slight ridge, as if for the attachment of a muscle, but there certainly is no muscle here: rarely the adductor ridge is only slightly prominent: there is a small and shallow little pit of variable depth for the lateral depressor muscle.

Tergum (2 k-2 o); this valve is here far more variable than in any other species: in the commonest purple-striped forms (2 l), the valve is rather broad, the basal margin lies in nearly a straight line on the opposite sides of the spur, which is placed at rather less than its own width from the basi-scutal angle; the spur is rather short, and in width about one fourth of the entire valve; its lower end is either bluntly pointed or more commonly nearly square (2 k) and parallel to the basal margin: in young specimens it is generally sharper than in older ones. Externally, in the line of the spur, there is either a slight longitudinal depression, or more rarely a deep furrow. The carinal margin is more or less convex, and is formed by upturned lines of growth: the scutal margin is broadly inflected. Internally, the articular ridge in the upper part is very prominent: the crests for the tergal depressor muscle are moderately prominent, but very variable. Sometimes the carinal portion of the basal margin is slightly hollowed out. In var. Stutsburi (2 m, 2 n, 2 o), and in some white varieties, which differ most in the shape of the tergum from the commoner varieties, the whole

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valve is narrower, the spur is much sharper and narrower, the carinal half of the basal margin is much hollowed out and slopes down towards the spur, with the crests for the depressor muscles depending beneath the basal margin, and with the carinal margin sometimes extremely convex or protuberant. But the shape and position of the spur, and the outline of the carinal half of the basal margin vary much in nearly all the varieties.

Compartments.—The upper parts of the parietal pores are either filled up solidly with, generally coloured, shell, or they are crossed by thin transverse calcerous septa: the longitudinal parietal septa occasionally bifurcate at their bases close to the outer lamina, making an irregular outer row of minute pores. The Radii have their septa rather fine, and finely denticulated on both sides, but sometimes only on the lower side; the thickness of the septa varies a little; the interspaces are filled up solidly; the summits of the radii are jagged and oblique, and usually form an angle of about 45° with the basis, not being added to above the level of the opercular membrane; but not rarely they reach up much higher, and are very nearly parallel to the basis, extending from tip to tip of the compartments. Again, in some ordinary varieties, and always in var. Stutsburi, the summits of the radii are extremely oblique, the radii themselves forming a mere border to the compartments to which they belong. In no other species have I seen so great an amount of variation in the form of the summits of the radii. The alæ, in like manner, have their summits either very oblique, not being added to above the opercular membrane, or they are only slightly oblique; it often happens that in those specimens in which the summits of the radii are nearly parallel to the basis, the alæ are very oblique, and the converse: in other individuals, both radii and alæ have equally oblique summits. The sutural edges of the alæ vary in thickness, being either very thin and obscurely crenated, or moderately thick and ribbed. The basis is porose; but I have never seen an underlying cancellated layer of shell, as is so common in several species.

Mouth: labrum, with from four to eight, generally with six, little teeth: mandibles with three teeth, and two minute lower teeth, or mere knobs: maxillæ with the edge straight, or with the inferior part forming a slightly step-formed projection. Cirri: the rami of the first pair are unequal by three or four segments, but in some specimens by five or six segments, with the front surfaces of the segments in the shorter ramus extremely protuberant. The second pair of cirri are short, with the front surfaces of the segments moderately protuberant: the third pair have a tuft of bristles at their bases on the thorax. The segments in the sixth pair have from four to six pairs of spines on the segments; equal-sized specimens seem to vary in this latter respect. There is a small sharp projection on the dorsal base of the penis.

Varieties.

With respect to var. 1, communis, I have nothing further to remark, except that I have seen specimens identically similar from the Medi-

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terranean, Natal, the Philippine Archipelago, and Sydney; at the latter place it is said to be rare, but in most places it is the commonest variety, and is often attached to ships' bottoms. Of var. 2, venustus, I have seen specimens from the west coast of Africa, Natal, and Ceylon, in groups by themselves, and associated with var. communis; it is much less common than var. 1. The third variety, pallidus, is not uncommon; I have seen many specimens from the bottoms of ships, from the West Indies, and the west coast of Africa. Of the var. 4, niveus, I have seen the most perfect graduated series passing into var. 1, both from the West Indies, Florida, and the Mediterranean: I have seen other specimens from the Red Sea and Madagascar. Of the var. 5, modestus, I have seen only one group from an unknown locality; it is only remarkable from its uniform colouring. The var. 6, Stutsburi, is more remarkable than the foregoing; until quite lately I did not doubt that it was specifically distinct; but as I have seen every character graduate into other varieties, I am now convinced that it is not a true species: all the specimens which I have seen have come on shells, or on ships' bottoms, from West Africa. Of var. 7, obscurus, I have seen three or four groups of specimens from unknown quarters, both on pebbles, shells, and on cork (probably from the Atlantic ocean); and likewise some specimens taken from the bottom of Her Majesty's ship "Fly," on the east coast of Australia; these latter are intermediate in character with the next var. variegatus, from the Australian seas, which I at first ranked as an undoubted species, but I have subsequently failed in discovering any sufficient diagnostic character. Lastly, of var. cirratus, I have seen several groups of specimens from India and the Philippine Archipelago, and a group intermediate in character between this and the first and third varieties, from Australia; I retained this variety owing to its peculiar freckled, pale brown colouring and beaded scuta (of which, however, I have seen decided traces in the common variety), as a distinct species, after I had given up all the foregoing forms. I entertain some doubts whether I have now acted right; but when I found some specimens which, I found it impossible to decide, whether to rank as amphitrite or cirratus, I determined to take the more prudent course, and sink the latter as a species. This variety, also, seems to connect B. amphitrite and concavus very closely.

21. BALANUS PŒCILUS. Pl. 5, fig. 3 a, 3 b.

Shell dull red, freckled with white. Scutum internally without an adductor ridge; tergum with the spur, sharply truncated, almost one third of width of valve.

Hab.—West coast of South America, Mus. Cuming; attached to an Avicula.

The appearance of the fragile shell, in the one group of

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specimens which I have seen, leads me to suspect that they may have grown under unfavorable circumstances. This species differs considerably in general aspect, but not much in essential characters, from B. amphitrite; the absence, however, of an adductor ridge to the scutum, and the sharply truncated spur of the tergum, are sufficient to distinguish them. In the opercular valves this species comes near to B. vinaceus, also from the west coast of South America; but the striated scuta of that species, the cancellated inner lamina of the parietes, the general colouring, and square porose radii, are amply diagnostic characters.

General Appearance.—Shell fragile, tubulo-conical, orifice large, passing from diamond-shaped into oval. Colour fine dark rose, freckled with transverse, sharply pointed, fine zig-zag white lines: the pink is also so arranged as to obscurely give to the walls a longitudinally striped appearance: radii generally rather whiter than the walls, and similarly freckled: terga similarly freckled: scuta dull red, with a white band along the scutal margin. Basal diameter of largest specimen half an inch.

Scutum, externally smooth: internally, articular ridge moderately developed, slightly reflexed: there is no adductor ridge: there is a distinct pit for the lateral depressor muscle. Tergum, with the scutal margin unusually prominent, toothed: longitudinal furrow shallow, the edges apparently having no tendency to fold in: spur short, barely one third of width of valve, with the lower end sharply truncated, parallel to the basal margin: articular ridge and crests for the depressores moderately prominent.

Compartments.—Walls very fragile, with the outer lamina not thicker than the inner lamina. Radii fragile, broad, with their summits moderately oblique; their sutural edges have the septa plainly denticulated on both sides, with the interspaces filled up solidly nearly to the tips of the septa. Alæ, with their summits more oblique than those of the radii; their sutural edges smooth. Basis with an underlying cancellated layer. Mouth: labrum with three unusually large teeth on each side of the notch: mandibles with the fourth tooth tolerably well developed, the fifth being confluent with the inferior angle. Maxillæ simple. Cirri,—first pair with one ramus longer by about four segments than the other ramus, which has considerably protuberant segments: second pair with segments only moderately protuberant: sixth pair with segments much elongated, but bearing only four pairs of spines.

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22. BALANUS EBURNEUS. Pl. 5, fig. 4 a-4 d.

BALANUS EBURNEUS. Aug. Gould (!) Report on the Invertebrata of Massachussetts, 1841, fig. 6.

Shell yellowish white. Scutum striated longitudinally: tergum with the spur truncated, the basi-carinal margin generally much hollowed out, and the carinal margin protuberant in the upper part.

Hab.—United States, from about lat. 42° to Charlestown; West Indies; Honduras; Venezuela; attached to shells and floating wood. Attached to ships' bottoms from Trinidad and Jamaica, associated with B. tintinnabulum, amphitrite, and improvisus. Brackish water, Salem, Massachussetts, according to Mr. Stimpson. Mus. Aug. Gould, Agassiz, Stutchbury, Cuming, W. Dunker, &c.; very common.

General Appearance—Shell conical, or almost tubular; white, with the surface very smooth, covered by thin yellowish epidermis, but with the radii naked. Orifice large, passing from rhomboidal into pentagonal, moderately toothed. Average full size, about one inch in basal diameter; I have seen a specimen 1.3 in basal diameter, and the same in height.

Scutum, plainly striated longitudinally: the teeth on the occludent margin small. Internally, the upper surface is roughened: the articular ridge is prominent, and either slightly or not at all reflexed: the pit for the adductor muscle is distinct; the adductor ridge is prominent in a variable degree, and is almost confluent with the articular ridge. In one specimen from Beverly Bay, U. S., the scuta were extraordinarily disintegrated, and I could perceive no trace of the external radiating striæ. Tergum, with the basal margin on the carinal side of the spur sometimes deeply (Pl. 5, fig. 4 b), and sometimes only slightly (fig. 4 d), and rarely hardly at all, hollowed out: when much hollowed out the valve may almost be said to be two-pronged, with the carinal prong narrower than the spur. There is no distinct longitudinal furrow, but the whole scutal margin projects above the general surface of the valve. In the carinal margin, in the upper part, there is a remarkable convexity or protuberance in the same plane with the valve, from which it is separated by a very slight and narrow ridge. The spur is about one fourth of the width of the valve, with its lower end abruptly truncated. Internally, the upper surface is much roughened with finely crenated ridges: the distinct crests for the depressores cover the whole of the so-called carinal prong.

Compartments: the radii and alæ have their summits oblique, sometimes a little rounded, but not smooth. The septa on the sutural edges of the radii are remarkably fine, and closely approximate; the

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denticuli are excessively minute. The sutural edges of the alæ are most delicately crenated; the alæ are largely added to during the diametric growth of the shell, and above the level of the opercular membrane. The parietal pores are square and rather large: they are crossed by transverse septa almost close down to the basis: the longitudinal septa have tolerably large denticuli at their bases. The pores in the basis are crossed by numerous transverse septa. When specimens grow in a group, the basis is sometimes irregularly cup-formed.

Mouth: labrum serrated with small teeth, decreasing in size downwards, on each side of the central notch. Mandibles with the third tooth rather thick and blunt, and with the fourth and fifth knob-like. Maxillæ, with the inferior part projecting much beyond the rest of the edge, and bearing two long single spines: between these two spines and the large upper pair, there are, in a full-sized specimen, about seven pairs of moderately long spines, feathered on their sides. Outer maxillæ thickly clothed with very fine spines, and remarkably prominent.

Cirri: first cirrus, with one ramus having twenty-six segments, and longer by ten segments than the shorter ramus, which has sixteen segments: the shorter ramus, and both rami of the second pair, have their segments remarkably protuberant in front; the protuberance, in the upper segments, equalling in length the supporting part of each segment: rami of the second cirrus unequal in length by five segments. Third cirrus with the segments only slightly protuberant; rami considerably longer than those of the second cirrus: at the dorsal base of the pedicel of this third cirrus there is no tuft of fine hairs, as is common in many other species. Sixth pair, with the upper segments elongated, bearing from six to seven pairs of spines; dorsal spines short, thin, and few.

Affinities: in external appearance of the shell, this species can hardly be distinguished from some of the white varieties of B. amphitrite; and there is a considerable resemblance, in some of the varieties, in the opercular valves; but the longitudinally striated scuta of B. eburneus suffice to distinguish these certainly very distinct species. Equally, or even more like externally, is this species to the B. Hameri, so that I have received from an eminent naturalist in the United States both species mingled in the same lot, all bearing the same name of B. eburneus; but when the internal structure of the shell is examined, the species are at once seen to be far removed from each other. Still more close is the affinity of this species to B. improvisus, both in internal and external characters: it agrees with this species in the singular habit of being able to live in brackish water: these two species are the only ones which have the labrum serrated with teeth, graduated in size, on each side of the central notch. In the case of young specimens of the var. assimilis of B. improvisus, an inhabitant of the same seas with B. eburneus, the diagnosis is most difficult without long practice; for in the young of eburneus, the compartments are only partially covered by yellow epidermis, and have a striped appearance, the radii are sometimes very oblique, the scuta externally have

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not acquired their longitudinal striæ, and internally the adductor ridge lies not so close to the articular ridge as it does subsequently; hence I for some time mistook the var. assimilis of B. improvisus for the young of B. eburneus. But I found in the latter, that the rami of the first pair of cirri, are always, even in the earliest youth, more unequal in length, and that each segment of the posterior cirri bears a greater number of pairs of spines, there being, even in very minute specimens, seven pairs. Moreover, after having examined scores of specimens, I found I could almost always distinguish the two species by the smoothness and curvature of the summits of the radii of B. improvisus; I entertain no doubt whatever about the distinctness of the two species; indeed, when both are mature, besides the greater size, striated scuta, &c. of B. eburneus, their general aspect is very different.

22. BALANUS IMPROVISUS. Pl. 6, fig. 1 a-1 c.

Shell white: radii narrow, with their upper margins smooth, slightly arched, very oblique. Tergum with a longitudinal furrow; spur with the end rounded.

Var. assimilis, with longitudinal white hyaline lines.

Hab.—England, Scotland, Belgium (?), Nova Scotia, United States, West Indies, Rio Plata, Southern Patagonia, Guyaquil, West Colombia; attached to wood, shells, rocks, ships' bottoms, from low tidal level to twenty fathoms depth.

General Appearance.—Shell conical, with a rather large diamond-shaped orifice, moderately or but little toothed; very smooth; walls never folded longitudinally; white, with an extremely thin pale-yellow persistent epidermis. The radii are very narrow, with their summits very oblique, rounded, and smooth; the epidermis is generally more persistent on the radii than on other parts, and this is exactly the reverse of what is common with B. eburneus. The specimens from nearly fresh-water in the R. Plata (hereafter to be mentioned), are brownish, and have undergone a remarkable degree of corrosion, the outer lamina of the walls having been entirely removed to near the base; hence the external aspect of these specimens is wholly different from ordinary individuals. The var. assimilis has also a very different appearance, owing to the dead white of the walls being relieved by narrow approximate longitudinal hyaline lines, corresponding with and caused by the longitudinal parietal septa being externally visible through the outer lamina of the parietes; the epidermis on the radii is also of a rather brighter yellow. The largest specimens which I have seen are those from the Plata, and those attached to a ship from the West Indies, and they had a basal diameter of .6 of an inch: from .4 to .5 of an inch is the more usual full average size.

Scuta, with the lines of growth but little prominent: articular ridge

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prominent, but little reflexed: adductor ridge straight and very prominent, varying a little in its distance from the articular ridge; there is scarcely any depression for the lateral depressor muscle; the upper internal surface of the valve is roughened with ridges. Terga, with a moderately deep longitudinal furrow; spur short, rather narrow, with the end rounded, placed at less than its own width from the basi-scutal angle; in the Rio Plata specimens the spur is close to this angle: the basal margin is generally straight on opposite sides of the spur, but sometimes on the carinal side it is a little hollowed out. The lines of growth are upturned along the carinal margin, which consequently is a little protuberant, but to a varying degree. The crests for the depressores are extremely distinct and prominent. In the varieties having the basi-carinal margin hollowed out, and the carinal margin protuberant, there is a marked resemblance to the peculiar tergum of B. eburneus.

Walls: the parietal pores are tolerably large, and are crossed by numerous transverse septa: the longitudinal septa are very finely denticulated at their bases, but occasionally almost smooth. The radii are, as stated, extremely narrow, and very remarkable from their smooth rounded edges; their septa are barely denticulated. The alæ are remarkably protuberant; they have their summits much less oblique than those of the radii, and sometimes they are almost parallel to the basis: their sutural edges are coarsely crenated. Basis, flat, thin, permeated by pores, but the pores do not generally run to the very centre; they are, as usual, crossed by transverse septa.

Mouth: the labrum is the most remarkable part; on each side of the central notch there are generally two teeth; and on the two sides of the notch itself nine or eleven smaller teeth, decreasing regularly in size downwards till they become so minute as to be hardly visible even under the compound microscope; thus, in the two specimens closely examined, there were altogether twenty-two and twenty-six teeth on the labrum. Mandibles with the two inferior teeth reduced to mere knobs: maxillæ with the lower part of the edge bearing two large spines, and generally, but not always, forming a step-formed projection. Cirri: the rami of the first pair are but slightly unequal; in one specimen examined there were fifteen segments in one ramus and twelve in the other: segments very protuberant in front. Second cirrus with the segments only slightly protuberant; segments thirteen. Third cirrus longer than the second pair, with the rami rather unequal in length: there is a tuft of long spines on the basal segment of the pedicel of this cirrus. Fourth cirrus twenty-two segments. Sixth cirrus, in the same individual, thirty-four segments: on each of these segments there are five or six pairs of spines. I may specify that the longer ramus of the first cirrus of a large Rio Plata specimen had twenty-four segments.

Varieties, affinities.—When I first met with the var. assimilis, misguided by its general aspect, I did not doubt that it was specifically distinct; I was strengthened in this view by the absolute identity of several hundred specimens attached to two vessels from Jamaica and Trinidad, in the West Indies, with one specimen from Charlestown, in

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the United States, sent me by Prof. Agassiz, and with several in three lots from the western tropical shores of South America: yet on close examination I can point out no one distinguishing character, either in the shell or animal's body, excepting the longitudinal hyaline lines on parietes, due to the septa being externally visible. The presence of similar lines is variable in white vars. of B. amaryllis and amphitrite, and they are seen in very young specimens of B. eburneus: hence it is impossible to consider so trifling a character as specific; moreover, lately I have seen a British specimen with hyaline lines, and some few other specimens in an intermediate condition. Under the head of B. eburneus, I have stated that although that species and B. improvisus, which in the West Indies are associated together, are most readily discriminated when old, yet when young, they so closely resemble each other that the eye requires much practice to separate them. On account of this species and B. crenatus being sometimes associated together on the shores of England, I have pointed out under B. crenatus, the relative diagnostic characters of the two. The chief affinity of B. improvisus is certainly towards B. eburneus; but in the narrow, oblique, rounded, and smooth-edged radii, there is a relationship shown to the species in the last section of the genus, such as B. amaryllis, and more especially to the fossil B. dolosus: so close is the resemblance in the external appearance of the shell, and in the structure of the opercular valves, to the latter species, that I for some time did not discover their distinctness. Balanus improvisus has hitherto been overlooked by naturalists, and has probably been confounded with B. crenatus or balanoides.

Range and habits.—This species, as far as my experience goes, is commoner on the shores of Kent than on other parts of England: the first specimens which I met with, I owed to the kindness of Mr. Metcalf, they were attached to wooden stakes from Herne Bay, together with a single specimen of B. crenatus: I have seen other specimens from near Woolwich, from the Kentish oyster-beds, from Sandwich, and from Ramsgate. The only other British specimens which I have seen are from the River Itchen, in Hampshire, and from Loch Shieldaig, in Ross-shire (Mus. Jeffreys), from a depth of twenty fathoms. This species is often attached to wood. At Ramsgate, the specimens were attached to a small coasting vessel, and they must have been immersed five or six feet; they were associated with B. crenatus, and with a few of B. balanoides. In the Brit. Mus. there are specimens collected by Mr. Redman, from Nova Scotia, in North America. When her Majesty's ship Beagle was beached at Santa Cruz, in Southern Patagonia, numerous specimens were found adhering to her copper bottom, some so small as to show that the species breeds in those latitudes. Near Monte Video, in the estuary of La Plata, I found many large, but much corroded specimens, adhering to some rocks in a small running stream of perfectly fresh water. The rise of the tide is here small, but at high water the specimens apparently were for a short time covered by the waters of the estuary, here itself only brackish, and occasionally almost fresh. I took home some specimens, and placing them in perfectly fresh water they continued for many hours expanding and retracting their cirri with perfect regularity and vigour. Here then we

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have a Balanus capable of living in fresh water, and likewise in the saltest seas: even brackish water is a deadly poison to several, probably to most, species of the genus; but this, as we have seen, is not the case with the allied B. eburneus. The water, I may add, at Woolwich, on the Thames, whence I have received B. improvisus, must at times be very brackish. I have already incidentally mentioned that the var. assimilis was attached in great numbers, associated with B. eburneus, tintinnabulum, and amphitrite, on vessels from the West Indies: one specimen sent me by Prof. Agassiz, from Charlestown, was attached to a specimen of B. eburneus; and, lastly, I have seen three sets of the same identical variety attached to shells from Guayaquil (in Mus. Brit. and Cuming), and from West Colombia. Here, then, we have the same species with an enormous range, from Nova Scotia and Great Britain to South Patagonia; and, which is the case with scarcely a single mollusc, it lives both on the eastern and western tropical shores of the South American continent.

23. BALANUS NUBILUS. Pl. 6, fig. 2 a-2 c.

Shell white, rugged: basis in parts imperfectly porose. Scutum with the articular ridge minute; adductor ridge prominent, forming a deep pit for the lateral depressor muscle: tergum with an internal patch of purple; apex produced, purple.

Hab.—California, Mus. Brit. and Aug. Gould; associated with B. glandula, and attached to wood.

I have seen two specimens of this species, brought by Lady K. Douglas from California; and two from Monterey, sent me by Dr. Aug. Gould. This is a very distinct species, coming nearer to B. porcatus than to any other species: it is also allied to B. cariosus. In the basis being in parts solid or not permeated by pores, it has claims to be placed in the next section, in which I at one time included it.

General Appearance.—Shell conical, rugged, sometimes furnished with sharp longitudinal ribs; dirty white. Orifice not large, oval, toothed. Radii rather narrow, with their summits oblique, much jagged. Basal diameter of largest specimen 2.1; height only 1.3 of an inch.

Scuta, broad, with the lines of growth prominent; internally, articular ridge very little prominent, sometimes hardly developed, but thick, ending downwards in a small free point. Adductor ridge

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prominent, blunt, produced straight downwards, making a deep longitudinal cavity for the lateral depressor muscle; in some specimens this cavity is almost arched over, so as to tend to be tubular, with a short ridge in the middle (Pl. 6, fig. 2 a): in other specimens there is no trace of this tubular structure. Terga, with the apex beaked, beak triangular, dull purple; the longitudinal furrow is so shallow as hardly to exist. The basal margin slopes down on both sides, with a nearly equable curvature towards the spur; hence the spur is broad in its upper part, and narrow at its obliquely truncated lower end. Internally, there is an elongated dark purple patch: the shallow articular furrow is of quite remarkable breadth; the articular ridge is medial, and the inflected scutal margin is not wide. The internal surface of the spur is formed into a ridge, which runs a little way up the valve, and is sometimes partially separated from the spur itself (fig. 2 c), making the basal extremity toothed or double. The crests for the depressores are pretty well developed.

Walls, moderately strong: inner lamina slightly ribbed: the denticuli on the bases of the parietal longitudinal septa are sharp: I could not see any transverse septa in the parietal tubes. The radii are rather narrow; their summits are remarkably jagged and very oblique; the septa are plainly denticulated on both sides, but chiefly on the lower side; each septum itself, towards the inner lamina of the radius, branches and divides: the interspaces are filled up nearly solidly. The alæ have apparently their summits less oblique than those of the radii: their sutural edges are finely crenated. The lower edge of the sheath is hollow underneath. The basis is flat; it is rather thin, and imperfectly porose; in parts it is not at all porose, in others it is traversed only by very minute pores: there is nevertheless, in some parts, even where the upper layer is not porose, an underlying, cancellated layer.

Animal's body unknown.

24. BALANUS CORRUGATUS. Pl. 6, fig. 3 a, 3 b.

Shell white, longitudinally folded; radii narrow. Scutum internally without an adductor ridge.

Fossil, Sub-Appennine formations; Colle in Tuscany; Mus. Greenough.

I have seen only two specimens of this species attached to rock, collected by Mr. Greenough, at Colle, and kindly given by him to me. The species comes near to the living B. crenatus, also found fossil in deposits of this same age; it differs, however, distinctly from that species, in having its basis permeated by pores, and, in a less degree, in the sutural edges of the radii being more plainly crenated: the

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opercular valves of the two species closely resemble each other. This may be the B. stellaris of Bronn, but it is futile attempting to identify the species of this genus merely by external characters, even when aided, as in this case, by an excellent drawing of the shell.

General Appearance.—Shell conical, with broad rounded longitudinal folds; orifice of moderate size, oval; radii narrow, with their upper margins oblique; but the summits of both specimens had been much broken. Colour, as it appears, originally white. Basal diameter of largest specimen 3/4 of an inch.

Scuta, with the upper portion much reflexed; the articular ridge is very prominent, and the articular furrow of great width; when the valve is viewed from the outside the articular ridge is very conspicuous: there is no adductor ridge. Terga, with the longitudinal furrow very slight; the spur is from one third to one fourth of the width of the valve, and its basal end is blunt and almost truncated; it stands about half its own width from the basi-scutal angle. Internally, the articular ridge is very prominent, and the articular furrow narrow and deep, extending down the valve in the line of the spur.

Parietes: the parietal tubes are remarkably large, and I think this can hardly be an individual peculiarity: the tubes are crossed by many transverse septa, close down to the basis. The radii are narrow, and have jagged, oblique summits: their sutural edges have very distinct septa, barely denticulated, with the interspaces filled up solidly. The alæ have oblique summits; I was unable to make out the structure of their sutural edges. The Basis is very distinctly permeated by pores, which are crossed by transverse septa.

The shell and opercular valves of B. corrugatus so closely resemble the same parts in B. crenatus, that I should not be much surprised at seeing the two species graduating into each other, if a larger series of specimens, from beds intermediate in age between the Sub-Appennine formations and the present time, were obtained. If indeed the basis of B. crenatus were permeated by pores, the two species could hardly be discriminated.

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Section D.

Parietes permeated by pores. Basis and Radii not permeated by pores.

——————

25. BALANUS PORCATUS. Pl. 6, fig. 4 a-4 e.

BALANUS PORCATUS. Emanuel da Costa. Hist. Nat. Test. Brit., p. 249 (1778).

LEPAS BALANUS. Linn. Syst. Naturæ (1767).

— — Born. Testacea Mus. Cæs. Desc., Tab. 1, fig. 4, (1780).

— — Chemnitz. Syst. Conch., 8 Band., Tab. 97, fig. 820, (1785).

BALANUS ARCTICA PATELLIFORMIS. Ellis. Philosoph. Transact., vol. 50, Tab. 34, fig. 18 (1758).

— SULCATUS. Bruguière. Encyclop. Method., Tab., 164, fig. 1 (1789).

LEPAS COSTATA and BALANUS. Donovan. British Shells, 1802-1804, Tab. 30, fig. 1, 2.

LEPAS SCOTICA. W. Wood. General Conchology, Pl. 6, fig. 3, sed non Lepas balanus, Pl. 7, fig. 3, (1815).

BALANUS ANGULOSUS. Lamarck (1818), in Chenu, Illust. Conch., Tab. 11, fig. 11.

— TESSELATUS. Sowerby (!). Mineral Conchology. Tab. 84 (1818).

— SCOTICUS. Brown. Illust. Conch. Great Britain, Pl. 7, fig. 2, sed non. Pl. 6, fig. 9 et 10 (1827); 2d edit., Pl. 53, fig. 1-3, 22, 23 et Pl. 54, fig. 1-3,

— GENICULATUS. Conrad. Journal Acad. Philadelphia, vol. 6, part 2, p. 265 (1830), Tab. 11, fig. 16.

— — Aug. Gould (!). Report on the Invertebrata of Massachussetts, fig. 9 (1841).

Shell white, generally sharply ribbed longitudinally: radii with their summits almost parallel to the basis. Scutum longitudinally striated: tergum with the apex produced and purple.

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Var. (a) Walls without longitudinal ribs. Mus. Brit., Cuming, Stutchbury, Jeffreys.

Hab.—South shores of England, Ireland, Scotland, Shetland Islands, Iceland, Davis's Straits, 66° 30´ N.; Lancaster Sound, 74° 48´ N. (Mr. Sutherland). Maine and Massachussetts, United States. China (?). In deep water, common on shells, crustacea, and rocks, sometimes imbedded in sponges.

Fossil in the glacial deposits of Scotland, Uddevalla, and Canada; in the mammaliferous and Red Crag of England; Mus. Lyell, Sowerby, S. Wood, &c.

General Appearance.—Shell conical, somewhat convex; white, sometimes tinted yellowish, from the thin investing membrane; the produced tips of the terga are purple: the parietes of each compartment have from two to four strong, prominent, sharp, straight longitudinal ribs; these are sometimes irregular, and rarely, as will presently be described, they are absent. The radii are smooth and of considerable breadth; their summits are nearly parallel to the basis or only slightly oblique: hence the orifice is entire; it is rather small and ovate, being broad at the rostral end, and very sharp and narrow at the carinal end.

Dimensions.—The largest specimens which I have seen from Great Britain or Ireland, have been 1.3 of an inch in basal diameter: in Mr. Cuming's collection, however, there was one much depressed specimen from the Shetland Islands, 2.1 in basal diameter: a regularly conical specimen from the coast of Massachussetts attained a nearly equal diameter; out of the glacial deposits in the Isle of Bute, Scotland, several specimens had this same diameter, namely, two inches, and were even more steeply conical, being 1.85 in height; some glacial specimens from Uddevalla and Canada, in Sir C. Lyell's collection, were 1.7 in basal diameter. Hence, it appears, as we shall presently see is likewise the case with B. crenatus and Hameri, that northern specimens, and those from the United States and from the glacial deposits, often exceed in dimensions those from Great Britain or Ireland.

Scutum: the lines or ridges of growth are broad and prominent; they are divided into square beads by fine striæ, radiating from the apex: and hence the valve is longitudinally striated. Internally, the articular ridge is extremely little prominent; the adductor ridge, or what must be called such, runs straight down under the articular ridge, making a deep longitudinal pit for the lateral depressor muscle. Tergum: the apex is a little produced, and coloured purple, as well as the upper internal surface of the valve; there is no longitudinal furrow, only a very slight depression: the spur is placed close to the basi-scutal angle; it is rather long, and measured across the upper part, is half as wide as the valve: its lower end is truncated and rounded; the basal margin slopes towards it. Internally, a very small portion of the scutal margin is inflected: the articular furrow is shallow and broad: the crests for the depressores are feeble. In young specimens the spur is bluntly pointed.

The Parietes (4 e) have large square parietal tubes: in the upper part these are filled up solidly without transverse septa: the longitudinal septa are finely denticulated at their bases, and the denticuli extend

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unusually close to the outer lamina. In very young specimens the inner lamina of the parietes is ribbed, in lines corresponding with the longitudinal septa, as is the case with most species of the genus; but in medium and large-sized specimens, there are between the ribs, thus produced, from one to four smaller ribs, which do not correspond with any longitudinal septa; they are finely denticulated at their bases, and may be considered as the representatives of longitudinal septa which have not been developed and reached the outer lamina. I have seen no other instance of this structure, namely, the presence of a greater number of ribs, on the inner lamina of the walls, than there are longitudinal septa. The radii have their summits generally parallel to the surface of attachment, as is usual in the first section of the genus, but sometimes they are slightly oblique: the septa sometimes rudely branch a little, but they exhibit scarcely a trace of denticuli: the interspaces are filled up quite solidly. The alæ have their summits very oblique; their sutural edges are finely crenated.

Basis, rather thin, translucent, not permeated by pores; obscurely furrowed in lines radiating from the centre: the circumference is marked in a peculiar manner by the longitudinal septa, and by the tips of those intermediate, denticulated ribs, which occur on the inner lamina of the parietes.

Mouth: labrum with six teeth: mandibles with the fourth and fifth teeth small and rudimentary: maxillæ, with a small notch under the upper pair of spines; in the lower part there is a single large spine. Cirri, dark brownish purple, making a singular contrast with the white operculum and shell; first pair, with one ramus, having twenty-six segments, and about twice as long as the shorter ramus, having twelve or thirteen segments, with their front surfaces protuberant. In the second pair the segments are but little protuberant: third pair about one third longer than the second pair: sixth pair, elongated, having in the same individual forty-six segments; these segments have shield-shaped fronts, bearing five pairs of spines, with some minute intermediate bristles. There is the usual point at the dorsal base of the penis.

Range: Geological History.—This species is common on the shores of Scotland and Ireland; the most southern point of Europe whence I have happened to see a specimen is Tenby, in South Wales: but I have no doubt it is found further south; and Mr. Jeffreys, who knows this species well, has found it common on the extreme southern shores of England. In the United States, it is found on the shores of Maine and Massachussetts: northward, I have seen specimens from Iceland, from Davis's Straits, and from Lancaster Sound, in lat. 74° 48´ north; these latter I owe to Sir J. Richardson. It is an inhabitant of deep water; in Mr. Thompson's collection there are several specimens from the Bay of Belfast, marked twenty-five fathoms, and one group said to have come from "about fifty fathoms, on the coast of Antrim:" one specimen from Cape St. Anne, Massachussetts, is marked as having come from only five fathoms. This species is commonly associated, on both sides of the Atlantic, with B. crenatus, and sometimes with B. Hameri and Verruca Strömia: mollusca, such as pectens, modioli, and oysters, offer the most usual surfaces of attachment: I have, however, seen many

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specimens on crustaceans, on rocks, and even on the roots of the larger sea-weeds. This species is very common in the glacial deposits of Uddevella, of Skien in Norway, and of Canada, and is associated with the same species as in the living state: I have seen, also, specimens from the same formation in the Island of Bute, Scotland. I have seen numerous specimens from the mammaliferous crag, and a few from the Red Crag of England. I owe to the kindness of Mr. J. de C. Sowerby an inspection of the original specimens of the B. tesselatus of the Mineral Conchology, which is certainly the present species.

Affinities.—This species is very distinct from every other; it comes nearest, as shown in all the characters derived from its opercular valves, to B. nubilus, and in this latter species we have seen the basis plainly tending to lose its pores and thus become solid. B. porcatus is perhaps allied in some degree to B. trigonus, and slightly to B. crenatus. The rather broad radii, with their summits hardly oblique, give this species a very different aspect from those species of the genus amongst which it must be placed.

Varieties: a conical specimen, sent to me from the coast of Massachussetts, is remarkable from the radii not having been at all developed, being represented by mere fissures. I have seen a few specimens of var. (a), (one collected by Sir E. Parry in the arctic seas) which had a remarkably different aspect from the common forms, but which, after a careful examination of the opercular valves and of the animal's body, I feel convinced are not specifically distinct: they are characterised by the walls being smooth and absolutely destitute of the external longitudinal ribs; by the shell being more cylindrical, with broader radii, and with the orifice larger and more rhomboidal; the walls and radii are much thinner, and the internal lamina is less plainly ribbed: the beak of the tergum is not purple. As most of these specimens had grown in a group crowded together, the difference of shape, and perhaps the thinness of the walls, is thus explained. In a specimen from Davis's Straits, in Mr. A. Hancock's collection, most of the above characters are in an intermediate condition; there are only a few external longitudinal ribs on the parietes; and the terga have not purple apices. In Mr. Cuming's collection there are some fine, brilliantly white specimens (without opercula) from the coast of China; these have thin walls and radii, and the walls are not longitudinally ribbed, but they are not smooth: the orifice is not large, nor the shape of the whole shell cylindrical. It is just possible that these latter specimens may be a distinct and representative species, but I do not think so.

26. BALANUS PATELLARIS. Pl. 6, fig. 5 a-5 c.

LEPAS PATELLARIS, (Gmelin). Spengler. Schriften der Berlin. Gesellschaft, &c. b. i (1780), Tab. 5; Chemnitz, Neues Syst. Conch., Tab. 98, fig. 839.

Shell depressed; brown, generally with obscure longitudinal

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violet stripes: radii (in full-grown specimens) with their summits rounded and surfaces finely ribbed parallel to the basis: basis sometimes permeated by imperfect pores. Scutum internally with an adductor ridge.

Hab.—Bengal, on wood, Mus. Brit.; on a shell, Mus. Stutchbury; Philippine Archipelago (young specimen), Mus. Cuming. According to Spengler, on the Coromandel and Malabar coasts.

General Appearance.—Shell depressed, sometimes much depressed: orifice elongated, rhomboidal, but little toothed; surface smooth, but in old specimens sometimes with the walls slightly folded longitudinally. The radii are rather narrow, with their summits oblique; in old specimens their summits are rounded, and their whole surface finely ribbed parallel to the basis. Colour, in old specimens dirty brown, tinged with violet, sometimes in longitudinal bands, and with whiter irregular marks in the upper parts owing to disintegration: in young specimens the walls are regularly banded longitudinally, with violet-brown and dirty white; the radii being generally of a paler dirty red or violet. Basal diameter of largest specimen .9 of an inch.

Scuta, externally rather smooth; internally, articular ridge prominent, reflexed, with the lower edge hollowed out so as to be slightly hook-formed: adductor ridge small; there is a slight pit for the lateral depressor. Tergum, with the spur bluntly pointed, placed at about its own width from the basi-scutal angle; there is no longitudinal furrow, only a slight depression; carinal margin arched and protuberant: internally, articular ridge extremely prominent, running down in the direction of the middle of the spur: crests for the tergal depressores well developed.

Parietes, with the pores rather large; the internal lamina is very strongly ribbed, the ribs being but slightly denticulated at their bases: the parietal pores do not appear to be crossed by transverse septa: sheath closely attached to the walls. The radii have jagged oblique summits forming an angle of about 45° with the horizon; in old specimens they become more oblique and narrow: and are then very remarkable from their summits being arched and rounded, with a crenated edge, and with their whole surface transversely ribbed in horizontal lines; this is likewise the case with the recipient furrow in the opposed compartments: in young specimens the radii are externally quite smooth: the septa on the sutural edges are bluntly denticulated; the interspaces being filled up solidly. The alæ have their summits oblique, but much less oblique than the summits of the radii; their sutural edges are very finely crenated.

Basis thin, either quite solid, that is, not permeated by pores, but only furrowed in lines radiating from the centre, or permeated by pores towards the circumference, the pores being of very small diameter;—so that we here have an important character variable within the limits of the same species. Base flat, and this holds good, as remarked by Spengler, even when the specimens are attached to cylindrical pieces of wood.

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Animal's body unknown.

Affinities.—In the basis being sometimes permeated towards the circumference by pores, and by the colouring (the other species in this and the next section being dirty white), B. patellaris has almost as strong a claim to be ranked in the last as in the present section: in the rounded summits of the radii, and in the state of the basis, it, perhaps, shows more affinity to B. improvisus than to any other species; it is, however, almost equally allied to B. glandula.

27. BALANUS CRENATUS. Pl. 6, fig. 6 a-6 g.

B. CRENATUS. Bruguière. Encyclop. Method. (des Vers) 1789.

LEPAS FOLIACEA, var. a, Spengler. Skrifter af Naturhist. Selskabet, b. i, 1790.

— BOREALIS. Donovan. British Shells, Pl. 160 (1802-1804).

B. RUGOSUS. Pulteney (?) Catalogue of Shells of Dorsetshire, 1799.

Montagu (?) Test. Brit. 1803.

Gould (!) Report on Invertebrata of Massachussetts (1841), fig. 10.

B. GLACIALIS (?) J. E. Gray. Suppl. Parry's Voyage, 1819.

B. ELONGATUS (!), CLAVATUS (!), Auctorum variorum.

Shell white: radii with their oblique summits rough and straight. Scutum without an adductor ridge: tergum with the spur rounded.

Hab.—Great Britain, Scandinavia, Arctic Regions as far as Lancaster Sound, in 74° 48´ N. (Mr. Sutherland); Behring's Straits (Captain Kellett); United States; Mediterranean; West Indies, (Mus. Brit.); Cape of Good Hope, (Mus. Krauss). Generally attached to shells and crustacea in deep water; sometimes to ships' bottoms. Very common.

Fossil in glacial deposits of Scandinavia and Canada, Mus. Lyell; in the mammaliferous, and Red, and Coralline Crags, Mus. S. Wood, J. de C. Sowerby, Bowerbank; Miocene formation, Germany, Mus. Krantz.

I find, in most collections, this species confounded with B. balanoides; I have even seen the two species, placed by Leach, on the same tablet in the British Museum: B. balanoides is, moreover, generally confounded with Chthamalus stellatus; nor has any one hitherto separated the present species from B. improvisus. On the other hand, trifling varieties, both of B. balanoides and B. crenatus, have commonly been considered as specifically distinct. From these

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facts it will be seen in what confusion our commonest British species of Balanus have been left. After due deliberation, I have little doubt that this is the B. crenatus of Bruguière, and probably the B. rugosus of Montagu, but this latter author omits all reference to the really important diagnostic characters between this species and B. balanoides. The B. crenatus is certainly the B. rugosus of Dr. Aug. Gould. In various collections, I find specimens of B. crenatus, when coming from the arctic regions, called B. glacialis, arcticus, and borealis; though I have not met with an authentic specimen of the B. glacialis of Gray ('Supp. Parry's Voyage,' 1819, p. ccxlvi), I have little doubt that it would prove to be the present species.

General Appearance.—White, usually of a dirty tint, from the yellowish or brownish persistent epidermis: conical, generally (fig. 6 a) with the parietes rugged and irregularly folded longitudinally; but sometimes much depressed and extremely smooth (6 b); often cylindrical and very rugged; occasionally club-shaped (6 c), the upper part being much wider than the lower: specimens in this latter condition sometimes have extremely narrow parietes, like mere ribs, and wide radii. The orifice in the cylindrical varieties is often most deeply toothed. The radii are generally narrow, and have jagged oblique summits; but not infrequently they are so narrow as to form mere linear borders to the compartments. The orifice is rhomboidal, passing into oval, either very deeply or very slightly toothed.

Dimensions.—The largest British specimen which I have seen was only .55 of an inch in basal diameter: specimens from Greenland and the northern United States frequently attain a diameter of three-quarters of an inch, and I have seen one single somewhat distorted specimen actually 1.6 of an inch in basal diameter. The specimens from the glacial deposits of Uddevalla and Canada appear, on an average, to attain as large or larger dimensions than those from the United States: on the other hand, the specimens from the mammaliferous and Red Crag are smaller, the largest being only .35 in basal diameter. When individuals have grown crowded together, their length is often twice, and even occasionally thrice, as great as their greatest diameter; thus I have seen a Greenland specimen 1.6 of an inch in length, and only .75 in diameter. In the British Museum there are some arctic specimens, one and a half inch in length, only half an inch in diameter at the summit (fig. 6 c), thence tapering downwards to a blunt point.

Scuta; the lines of growth are but little prominent: the surface is generally covered by disintegrating membrane. The upper ends are usually a little reflexed, so that the tips project freely as small flattened points. Internally, the articular ridge is highly prominent and somewhat reflexed: there is no adductor ridge, but a very distinct impression for the adductor muscle: the depression for the lateral depressor

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muscle is small, but variable. The terga are rather small: the spur is short, and placed at rather less than its own width from the basi-scutal angle; the basal margin slopes a little towards the spur, of which the lower end is rounded or bluntly pointed in a variable degree. There is no longitudinal furrow, hardly even a depression. Internally, the articular ridge is very prominent in the upper part: the crests for the tergal depressores are well developed, but variable.

Compartments.—The internal carinal margin of each compartment, from the sheath to the basis, generally, but not invariably, projects a little inwards beyond the general internal surface of the shell, in a manner not common with the other species of the genus: the basal edge of this projecting margin rests on the calcareous basis, and is crenated like the basal edges of the longitudinal parietal septa. The whole internal surface of the shell is ribbed, but the ribs are not very prominent. The parietal tubes are large, and are crossed in the upper part, and often low down, by transverse thin septa: the longitudinal parietal septa are only slightly denticulated at their bases; occasionally they divide at the basis close to the outer lamina of the parietes, making some short outer subordinate pores. In the circular furrow beneath the lower edge of the sheath, there are sometimes little ridges, dividing it into small cells: sometimes, however, this furrow is filled up by irregular knobs of calcareous matter. The radii are always rather narrow, and often they form mere linear ribbons of nearly uniform width along the edges of the compartments. Their summits or edges are always more or less irregular and jagged: they form an angle with the horizon of generally above 40°. Their septa are fine, and barely or not at all denticulated. The alæ have oblique summits: their suteral edges are rather thick and distinctly crenated. Basis flat, calcareous, very thin, with the surface slightly marked by radiating furrows, which furrows answer to the radiating pores that occur in the bases of most species. In a club-shaped arctic specimen, one inch and a half in length, the summit being half an inch and the base only one fifth of an inch in diameter, the basis was still calcareous, thick, and not permeated by pores.

Mouth: labrum with six teeth: mandibles with the fourth tooth minute or rudimentary, and the fifth generally confluent with the inferior angle. Maxillæ with generally, but not invariably, a small notch under the upper pair of great spines. Cirri, first pair with the rami very unequal in length, one ramus being nearly twice the length of the other; in a large specimen having a cylindrical shell the proportional numbers of the segments in the two rami of the first cirrus were ten to twenty-three; in a small conical specimen the numbers were only eight to thirteen. The second cirrus has only two or three more segments than the shorter ramus of the first pair: the third cirrus has one or two more segments than the second; but it is nevertheless decidedly longer than the second. On the dorsal surfaces of both segments of the pedicel of the third cirrus, there is a tuft of fine spines. The segments of these three pairs of cirri are not much protuberant in front. The segments of the posterior cirri have, each, four, or five, or six pairs of spines. Penis, with a straight, sharp, short point on the dorsal basis.

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Range, habits, &c.—I have received specimens from all parts of the coast of Great Britain and Ireland, generally attached to crustacea and mollusca, and never hitherto from rocks uncovered by the tide. This species is also attached to floating timber, sticks, fuci, and occasionally to pebbles at the bottom of the sea. Mr. Thompson has sent me specimens from twenty-five fathoms depth in Belfast Bay: others on a Pinna from about fifty fathoms on the coast of Antrim; others from between three and six fathoms attached to Laminaria digitata: there is a specimen in Mr. Jeffreys' collection marked forty-five fathoms. It is often associated, both on the coasts of America and Britain, with B. porcatus, and though these species are so distinct, yet when both have their surfaces similarly affected by being attached, as is often the case, to large Pectens, it is not at first easy, by external characters, to distinguish them, except by close inspection of the terga, which in B. porcatus are beaked and purple. The B. crenatus is sometimes associated in deep water with B. Hameri. At Ramsgate, in Kent, I saw a rudder of a ship, in which the two or three upper feet were thickly coated with B. balanoides, and the two or three lower feet with B. crenatus and improvisus mingled, together with a few of B. balanoides: occasionally vessels are thickly incrusted with this species, but I have never seen an instance of its concurrence with B. tintinnabulum and amphitrite—the commonest species on ships coming from the south. I have seen specimens from Greenland, Baffin's Bay, the coast of Labrador, and other specimens marked simply, "Arctic regions," and, again, others from the shores of Maine and Massachussetts. The arctic specimens, and those from the northern United States, are larger than the British. I have seen one single minute specimen on a crab, marked as having come from the Mediterranean. In the British Museum, amongst some specimens of B. eburneus, ticketed as having been sent from Jamaica, there was a small group of specimens, differing in no one essential respect from the common varieties of B. crenatus: at first I concluded that this was an erroneous habitat, and that the specimens had really come from the United States, where B. eburneus, is found as well as in the West Indies: for it appeared to me exceedingly improbable that an animal which can exist in lat. 75° N. should inhabit the hot shores of Jamaica: but subsequently I have received a specimen from Prof. Krauss, collected by himself in Algoa Bay, which is perfectly characterised, and even has the little cells in the furrow under the sheath: so that I am compelled to admit this enormous range and capability of resisting the most extreme climates. That this species should live in the tropical seas is the more surprising, as the large size of the specimens in the northern seas and in the glacial deposits, might fairly have been supposed to have indicated special adaptation for a cold climate. The great geographical range of this species accords with its range in time from the present day to the Coralline Crag period.

The specimens from the glacial deposits which I have examined, chiefly in Sir C. Lyell's collection, are very fine and large; they are often associated, like the now living individuals, with B. porcatus and Hameri; they come from the well-known formation of Uddevalla and

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from Canada. There are well-characterised specimens in the mammaliferous Crag, at Bramerton and near Norwich, in Sir C. Lyell's collection, and from Sutton and other places in the Red Crag of the eastern shores of England: these specimens are decidedly not only smaller than the glacial, but than the recent English specimens; for the largest Crag specimens which I have seen had a basal diameter of only .35 of an inch. The specimens which I have seen from the Coralline Crag, and some others sent me by Krantz from the miocene formation of Flonheim bei Abzei, in Germany, had not their opercular valves, yet I cannot doubt, considering how few species there are in the present section of the genus, that I have rightly identified them.

Diagnosis.—Under the head of B. balanoides I shall make a few remarks on the diagnosis between that and the present species; as B. improvisus is found on the British shores, sometimes mingled with B. crenatus, I may observe that, externally, the only difference consists in the edges of the radii in B. improvisus being much smoother and rounded, and in the whole shell being less rugged. Internally, in B. improvisus the porose basis, the presence of an adductor ridge on the under side of the scutum, the graduated teeth on each side of the central notch in the labrum, and the little inequality in length of the rami of the first pair of cirri, are clearly and amply diagnostic.

28. BALANUS GLANDULA. Pl. 7, fig. 1 a, 1 b.

Shell white; parietes with the internal lamina generally strongly ribbed longitudinally, with the pores imperfect and small, sometimes in part absent; radii narrow, with their summits rounded. Scutum with an adductor ridge; tergum with the spur truncated and rounded.

Habitat.—California, Mus. Cuming, Aug. Gould; attached to shells and wood, together with B. nubilus. Southern Pacific ocean, attached to Pollicipes polymerus, Mus. Brit.

General Appearance.—Shell steeply conical, or cylindrical and elongated; dirty white; walls rugged, longitudinally folded; radii narrow, with their summits very oblique and rounded; orifice toothed. Basal diameter of largest specimen half an inch.

Scutum, resembling externally that of B. crenatus; rather broad, surface smooth; articular ridge very prominent, and articular furrow very wide; hence, when the summits of the opercular valves are worn down, the two scuta together form a square projection indenting the two terga, as in B. balanoides. Internally, there is a small adductor ridge, on the lower side of which there is a pit, as if for a muscle. The depression for the lateral depressor muscle is small, but variable. Tergum without any longitudinal furrow, and hardly a depression: spur

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broad, with its lower end truncated and rounded; internally, articular ridge very prominent; crests for the depressores well developed.

Compartments:—The internal surface of the parietes is smooth in the upper part beneath the sheath, but generally very strongly ribbed in the lower part, the ribs being plainly denticulated at their bases; in other specimens, the ribs are very small, and even in parts quite obsolete. The parietal pores are short and imperfect, sometimes reduced to an extremely minute size, to be detected only when the walls are broken across near the basal edge, and most carefully examined; occasionally not even a trace of a pore exists. Hence in this respect, this species offers a singular case of variation. The radii are narrow, and of nearly the same width from top to bottom; their very oblique summits, when well preserved, are smooth and rounded: their sutural edges are ribbed or crenated with extremely fine, smooth septa; the recipient furrow is plainly marked by these septa. The sutural edges of the alæ are crenated; their summits are less oblique than those of the radii.

Basis, thin, finely furrowed in lines radiating from the centre; margin sometimes deeply sinuous.

Mouth: labrum with the central notch rather widely open, with four teeth on each side of it: palpi with very short spines along their inner margins: mandibles with the fourth and fifth teeth forming mere knobs: maxillæ small, with a mere trace of a notch under the two great upper spines. Cirri; first pair with the rami unequal by three or four segments, the longer ramus being only one quarter of its own length longer than the other ramus. Second pair short, with the segments (and those of the shorter ramus of first pair) somewhat protuberant. Third pair with the rami one third longer than those of the second pair. Sixth pair with the upper segments elongated, and bearing six or seven pairs of spines.

Affinities.—This species in general appearance closely approaches B. crenatus and balanoides, and it is related to them in many essential parts, such as in the opercular valves. It agrees with B. balanoides, and differs from B. crenatus, in the smallness and imperfection of the parietal pores, and in the radii having rounded summits; it agrees with B. crenatus in the structure of its basis, and in the prominent longitudinal ribs on the internal surface of the parietes, and differs from that species in the spur of the tergum being squarer, and in the scutum having an adductor ridge.

Range.—From the appearance of the Californian specimens, I suspect that they had adhered to tidal shells and to wood. The specimens in the British Museum, adhering to Pollicipes polymerus, consist of two lots, one of unknown origin, and the other certainly brought from the southern half of the Pacific Ocean by Sir James Ross: it deserves notice, that the Pollicipes polymerus, the supporting object, ranges from California to the southern Pacific Ocean.

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Section E.

Basis membranous.

——————

29. BALANUS BALANOIDES. Pl. 7, fig. 2 a-2 d.

LEPAS BALANOIDES. Linn. Fauna Suecica, 1746, et Syst. Naturæ, 1767.

— — O. Fabricius. Fauna Groen., p. 424, 1780.

— — ET CLAVATUS. Montagu (!). Test. Brit., 1803.

BALANUS VULGARIS (?) Da Costa. Hist. Nat. Testacea, Pl. 17, fig. 7, 1778.

— OVULARIS ET ELONGATUS. Aug. Gould (!). Report, Invertebrata of Massachussetts, figs. 7 and 8, (1841).

— PUNCTATUS, CYLINDRICUS, ELONGATUS, FISTULOSUS CLAVATUS. Auctorum variorum. Sed non B. punctatus, Bruguière, Encyclop. Method., et non B. punctatus, Montagu, Test. Brit.

Parietes either solid, or cancellated, or rarely formed by a single row of pores. Tergum, with the spur bluntly or sharply pointed.

Var. (a) with the parietes permeated by tubes; spur of tergum sharply pointed; segments in the posterior pairs of cirri, bearing from eight to ten pairs of spines.

Habitat.—Great Britain, France, Norway, Shetland Islands; Greenland, according to O. Fabricius; North America, in lat. 66° 34´ N.; Labrador; Nova Scotia; Massachussetts, Delaware. Extremely common, attached to rocks, shells, and wood, within the tidal limits.

I have no doubt that the present species is the Lepas balanoides of Linnæus; though O. Fabricius is the only author who gives, in his "Fauna Groenlandica," a sufficient description for the species to be recognised with certainty. I believe this also is the B. balanoides of Bruguière, though he is in error, as far as my experience goes, in stating that

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the basis is ever calcareous. I have little doubt, also, that this is the B. vulgaris of Da Costa. The B. balanoides, in its corroded and therefore punctured state, is certainly the B. punctatus of most British collections; but I do not believe it is the B. punctatus of Montagu, which I have scarcely any doubt is the Chthamalus stellatus, so often found in the southern shores of England, and even in some of the best arranged collections, mingled with our present species.

General Appearance.—The shell, in middle-sized and old specimens, is almost invariably folded longitudinally and irregularly; it is either dirty white or very often pale brown, and punctured from the outer lamina having been corroded, to which action it is extremely subject. In very young specimens, the surface is usually quite white and smooth. The shell is sometimes much depressed; generally conical, but when crowded together, cylindrical or club-shaped, one specimen being even more than five-and-a-half times as long as wide. In Mr. Jeffreys' collection there is a specimen 2.5 of an inch long, .45 in diameter at the summit, only .2 in the middle, and rather more than .2 near the base. Another specimen was 1.8 in length, its greatest diameter being .35 of an inch at the summit. On the other hand, I have seen a very depressed variety, with deeply folded walls, in Mr. Thompson's collection from near Dublin, which was no less than four times as wide as high; so that the difference in proportion of height and greatest width, in the two extreme specimens, was nearly as 10 to 1. Occasionally, from some unknown cause, isolated specimens become cylindrical. The orifice of the shell, in the much elongated specimens, is generally deeply toothed. The radii are always narrow, sometimes extremely narrow, and have their summits smooth and rounded.

English specimens do not usually attain half an inch in basal diameter; I have, however, seen one from near Yarmouth .9 of an inch in diameter. Specimens from Massachussetts seem rather larger than the average size of British specimens, many being .6 of an inch, and one specimen a whole inch in basal diameter.

The opercular valves so closely resemble those of B. crenatus, that the description is necessarily comparative; in some cases they could hardly be discriminated; generally, owing to the disintegration to which this species is subject, the tips of the scuta are worn off, and hence the articular ridges together form (Pl. 7, fig. 2 a) a square projection, indenting the two terga; but I have examined young specimens and others when not disintegrated, in which the opercular valves, viewed externally, presented no difference whatever from those of B. crenatus. The scuta, however, are, I think, generally rather thicker, with the growth-ridges more prominent, and with the tips certainly less reflexed than is usual with B. crenatus. Internally, the articular ridge is rather less prominent: there is no distinct adductor ridge. The terga are often rather narrower in proportion, and this especially holds good

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in the elongated varieties; in these latter, there is occasionally a moderately deep longitudinal furrow: the spur is often exactly the same shape as in B. crenatus, but it is apt to be rather longer (Pl. 7, fig. 2 c) and more pointed: in var. (a) it is pointed (fig. 2 d) in a very remarkable manner. Internally, the articular ridge is decidedly more prominent than in B. crenatus; the crests for the tergal depressor muscles are either well developed or almost absent. From this description it will be seen, how singularly the opercular valves of the common varieties of these two species resemble each other. I may mention that in some of the much elongated specimens, the muscles going to the opercular valves partially lose their transverse striæ, and become ligamentous.

The Parietes are either quite solid, or more commonly are permeated by minute pores, or by small irregular square tubes (Pl. 7, fig. 2 b), which only run up each successive zone of growth, for very short distances, giving to the shell a cancellated structure, which from corrosion is often externally visible. In the rather rare variety (a) the parietes are permeated by regular tubes, extending up to the apices of the compartments, but crossed by transverse septa. The longitudinal septa, when such can be said to occur, in no case are denticulated at their bases. The internal surface of the parietes is either quite smooth or is traversed (Pl. 7, fig. 2 b) by very slight anastomosing ridges, but never, even in var. (a), by regular longitudinal ribs, as in most other species. The carinal margin of each compartment, on the inside, projects, as in B. crenatus, inwards, beyond the general surface of the shell, and running down, rests on the basal membrane. The lower edge of the sheath is rarely hollow beneath. The walls are lined by purplish, or pale brown, or sometimes by almost black corium; numerous tubuli penetrate the under sides of the walls and opercular valves; and it is the intersection of these tubuli that gives the punctured appearance to the often corroded surface of the shell. The radii are narrow, generally very narrow; they have their upper and outer margins, as seen externally, very oblique, rounded and (when well preserved) smooth; their sutural edges are either quite smooth, or sometimes just perceptibly pitted, like the basal margin of the walls, or occasionally furnished with globular or arborescent little ridges. The alæ are also very oblique, but to a variable degree, sometimes only slightly oblique: their sutural edges are either smooth or obscurely crenated. Basis, membranous; in some much elongated specimens, during continued growth, the basal edges of the compartments approach each other so closely as almost to touch, so that the whole shell becomes pointed at the bottom; but on careful inspection I have never failed to find, even in the most pointed specimens, a minute basal membrane; in other much elongated varieties, in which the shell has apparently become too large for the animal's body, the basal membrane, instead of being flat, becomes drawn up deeply inwards, so as to touch the surface of attachment only close round the basal edges of the shell.

Mouth: labrum with the teeth on each side of the central notch unusually variable in number; I have seen specimens with only two on each side, with four on each side, with five on one side and four on

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the other, with five on one side and none on the other, and with six on both sides; hence the total number ranges from four to twelve. Mandibles, with the fourth and fifth teeth small, or quite rudimentary. Maxillæ, with scarcely even a trace of a notch under the upper pair of spines. Cirri; first pair, with one ramus one third or one fourth longer than the other; in one specimen the number of segments were nine and sixteen in the two rami: second and third cirri short, very nearly equal in length, having in the just-mentioned specimen respectively ten and eleven segments; the sixth cirrus in this same specimen had twenty-five segments, each segment being about as long as broad, and supporting six pairs of spines. In the singular variety (a) the posterior cirri are more elongated, and each segment supports seven or eight, and in one case even ten pairs of spines! the third pair is also in this variety proportionally rather longer. At the base of the third pair there is a tuft of fine spines. The penis has not, as in B. crenatus, a point at its dorsal basis. The branchiæ are very little plicated.

Varieties.

Of the varieties having much elongated, club-shaped, hour-glass shaped, and depressed shells, there is no necessity to say anything in particular. With respect to the remarkable variety (a), I at first named and described it as a distinct species: I have received two lots, both from North America, one being sent me by Professor Agassiz from Cape Cod. These agreed in having the parietes permeated by regular tubes; in having the spur of the tergum most sharply pointed; in the third pair of cirri being proportionally longer compared with the second pair; in the sixth pair having more numerous segments, namely, three times as many as in the third pair; in the segments of the posterior cirri being more elongated, and especially in the number of pairs of spines on each segment—amounting in one case even to ten, a number unparalleled in other cirripedes. It may naturally be asked why I have not retained so well marked a form as a distinct species? In the first place, I found the most remarkable character in var. (a), namely, the number of pairs of spines on the posterior cirri variable, there being in one lot seven or eight pairs, and in the other lot nine or ten pairs on each segment. Secondly, all the characters by which this variety differs from the common B. balanoides, are those which are variable in the latter; this is especially the case with the structure of the parietes, and in a lesser degree with the spur of the tergum. Thirdly, I found a specimen in Mr. Cuming's collection, from Sweden (so that this var. (a) is not confined to North America), in which the cirri quite resembled those of the American specimens, but the spur of the tergum was in an intermediate condition as compared to that of ordinary varieties; and the parietal tubes were of unequal sizes, and scarcely more regular than sometimes in the true B. balanoides. And lastly, I have seen specimens from Ayrshire, with the parietes permeated by regular tubes, but with the tergum in an intermediate condition, and with the segments of the posterior cirri not more numerous or more elongated than in B. balanoides, supporting only six or seven pairs of spines, that is only one more than is common with B. balanoides; so that it was impossible to decide whether to rank the Ayrshire

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specimen under var. (a) or under the common form, so that I was compelled to give up var. (a) as a species.

Monstrous individuals, with the male organs aborted: Parasite.— Amongst some specimens, chiefly elongated ones, sent to me from Tenby, in South Wales, I found no less than seven individuals with some of the posterior cirri distorted, unequal on the opposite sides, and in an almost rudimentary condition, and in each case with the penis truncated, without any muscle entering the stump, which was absolutely imperforate: the vesiculæ seminales were much shrunk; in one case without any zoosperms; in another case with headless zoosperms cohering in an unusual manner; hence it is certain that these individuals were functionally only female, and could not impregnate their own ova; yet in two instances the ova had been impregnated, no doubt by neighbouring perfect individuals, for they contained well-developed larvæ. Several of these monstrous individuals were infested by one, two, or three curious crustaceans, which have been described by Mr. Goodsir,* as the male of the Balanus; but these supposed males are females, and were distended with ova containing almost mature larvæ; I believe that they are the females of the unnamed genus, belonging to the family of Ioniens, described by Mr. Goodsir, which live parasitic within the sack (as I likewise found) of the same individual Balani.

Diagnosis.—I have seen several specimens of this species and of B. crenatus, absolutely undistinguishable in external appearance. I may specify one of B. balanoides, imbedded in an alcyonidium, and one of B. crenatus, imbedded in a sponge, and therefore neither at all abraded. Generally, the tips of the scuta in B. crenatus are a little reflexed, whereas in B. balanoides, when the shell has been at all disintegrated, the tips form a square projection locked into the terga. Bal. crenatus never assumes the punctured appearance so common in B. balanoides. Very young specimens of the latter can be distinguished by their dead white colour and smoothness. The edges of the radii are almost always smoother than in B. crenatus, and they are never so wide as is sometimes the case with B. crenatus. When a specimen is disarticulated, our present species can at once be distinguished from B. crenatus (and from B. improvisus), by its membranous basis, and by the solid or cancellated walls, which are rarely permeated by regular tubes or pores; and the walls when porose are not internally ribbed. I have already pointed out the few very trifling points, in which the opercula of the two species differ. The mouth and cirri offer likewise very few differences: in B. balanoides there are often more teeth on the labrum than in B. crenatus; the rami of the first cirri are perhaps here rather less unequal; the second and third pairs of cirri are certainly in most cases more equal in length; and lastly, the segments of the sixth cirri, even in the common varieties, bear, in equal-sized specimens, more pairs of spines than in B. crenatus. We shall see that in habits, with regard to depth, the two species differ, B. balanoides inhabiting much shallower water than B. crenatus.

Range, Habits, &c.—This species is extraordinarily abundant within

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* 'Edinburgh New Philosophical Journal,' July, 1843.

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the tidal limits round the shores of Great Britain, and apparently of the northern United States. Besides numerous specimens sent to me from very many English localities, the late Mr. W. Thompson, of Belfast, kindly placed in my hands his very large collection; from these materials it appears that B. balanoides is the only tidal species in the northern parts of our island; but in the south and south-west, it is associated with the Chthamalus stellatus and Balanus perforatus. I doubt whether this species ever lives below the lowest tides; the case of a few specimens being mingled with B. improvisus and crenatus, (mentioned under the latter species,) at the bottom of a rudder of a small vessel, about six feet deep, is hardly an exception, for the water would there be troubled and aërated almost as in a breaker; and on this very rudder the upper two or three feet were coated exclusively by the B. balanoides. This species lives on rocks at both the uppermost and lowest limit of the tides; I am informed by Mr. Thompson, that he has seen specimens attached to a spot not covered by water during neap-tides. As a proof of its tenacity of life, Mr. Thompson informs me that he accidentally kept some specimens in a box, in a warm sitting-room, and found them alive seven days afterwards. This same most accurate observer finds, however, that B. balanoides is very susceptible to brackish water; he says, "that having kept some specimens alive for a week in excellent health, the water being changed once in thirty-six hours, they were one day killed instantly by some water, though brought from the same part of the estuary as usual, having been rendered brackish by much rain having lately fallen." I may recall the fact, that B. improvisus lives daily for hours in absolutely fresh running water.

The B. balanoides lives attached, often continuously coating many square feet of the surface, to rocks, pebbles, wooden-piers, littoral shells and ulvæ. The most northern point whence I have received specimens, is in lat. 66° 34´ in North America, collected by Mr. Sutherland; and the most southern point is Delaware Bay, in the United States, in lat. 39°; I do not believe that this species extends into the Mediterranean, for Ranzani (Mem. di Storia Nat.), who particularly attended to the nature of the basis, was not acquainted with any Balanus having a membranous basis; and Poli (Test. Ut. Siciliæ,) describes only two species thus characterised, and these are manifestly Chthamali.

With respect to the rate of growth of this species, I am indebted to Mr. W. Thompson for the following note:—

"Sept. 29, 1848.—I examined a great number of Balani, in reference to the growth made by them during the present season, and found it to average three lines in diameter, and at most four lines. I saw a few minute specimens, only one line in diameter, showing that the species continued to breed until lately: these latter were probably not more than four weeks old. The young of the present year are plainly distinguished from the older ones, by their pure white colour and fresh appearance. Judging from the size of this year's specimens, and of

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the older ones on the same stones, I am of opinion that the term of life of the species is two years. Of the older shells, which I examined and found living in the spring, nine tenths are now dead, the walls only remaining, the opercular valves having been washed away."

Mr. Thompson goes on to say, that the individuals which had, on July 3, a basal diameter of from two and a half to three lines, had attained, by the 30th of September, a diameter of four and a half lines, this being here the maximum size of the species.

30. BALANUS CARIOSUS. Pl. 7, fig. 3 a-3 e.

LEPAS CARIOSA. Pallas. Nova Acta Acad. Scient. Petrop. tom. ii (1788), p. 240, Tab. 6, fig. 24.

Parietes thick; formed by several rows of unequal-sized pores. Tergum narrow, with the apex beaked, and spur sharply pointed.

Hab.—Columbia River, west coast of North America, Mus. Brit. and Cuming; Behring Straits (Capt. Kellett); the Kurile Islands, according to Pallas. Attached to shells, and to each other in groups.

General Appearance.—Shell steeply conical, with a rather small oval orifice; or cylindrical, with a large rhomboidal and little toothed orifice. Colour dirty white. Surface either simply rugged, or more commonly covered by numerous, narrow, extremely prominent, longitudinal plaits; from the manner in which these overlap each other, the shell almost appears as if thatched with straw. The upper corroded part of the shell usually exhibits a cancellated and finely punctured surface. The radii are generally very narrow, forming towards the base of the shell a mere narrow ribbon to each compartment, and often hardly distinguishable; but in one specimen they were of considerable width: in the former case, the alæ are often widely exposed. The largest specimen which I have seen was 1.5 of an inch in basal diameter, but Pallas gives 2.2 as the measurement of a specimen from the Kurile Islands.

The opercular valves are united to each other and to the shell by unusually strong membrane; and the upper parts of both valves, in all the specimens seen by me, have been much disintegrated. The Scutum, in old specimens, is faintly striated longitudinally, but in some there is hardly a trace of this: the occludent margin is furnished with a few large knobs, not corresponding with every alternate line of growth (as is usual with other species), but with every fourth or fifth line. Internally, the articular ridge is moderately prominent (in young specimens more prominent) and reflexed. The adductor ridge is sharp and

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prominent; in the upper part it is confluent with the articular ridge, but in young specimens can be seen to be distinct; in the lower part it borders a large deep cavity for the lateral depressor muscle, in the middle of which there is a very slight longitudinal ridge; this cavity sometimes is almost closed or arched over in its upper part. In one specimen, the basal margin of the scutum was deeply hollowed out in the middle. The Tergum is remarkably narrow, with its apex produced into a triangular beak, hollow within, and sometimes faintly tinged purple. A deep, closed, longitudinal furrow runs down the valve. The spur is long, remarkably narrow, and pointed. Internally, the spur is produced up the valve as a ridge: the inflected scutal margin, and the prominent articular ridge, are both nearly straight, and parallel to the spur. The crests for the depressores are sharp and very prominent.

The Parietes are very thick and strong: unlike every other species of the genus, they consist of several very irregular rows, of unequally sized, round or angular tubes (3 b). These tubes or pores are generally short, and are at frequent intervals crossed by transverse septa; they often rather deserve to be called cells than tubes. New tubes are formed along the inner as well as along the outer lamina. They are lined by dusky purple corium. The internal surface of the parietes is smooth in the upper part, and in the lower, it is reticulated by slight, irregularly branching ridges. The carinal internal margin of each compartment projects a little, as in the case of B. crenatus and balanoides. The lower edge of the sheath is either hollow beneath, or is united to the walls. The radii in one specimen were broad, with slightly oblique, jagged summits; generally they are extremely narrow, forming mere ribbons along the lower edges of the compartments, barely extending up as high as the sheath. They can sometimes hardly, or not at all, be seen, until the shell is disarticulated: in rather young specimens the sutural edge is sometimes quite smooth; in old specimens the lower part of the edge has coarse arborescent septa, with the interspaces filled up solidly, whilst the upper part is smooth. The alæ are conspicuous from the outside, owing to the little development of the radii; but owing to the diametric growth not having been great, the part added during such growth is narrow; the summits of the alæ are only slightly oblique: the sutural edge is coarsely crenated, with the teeth denticulated or slightly arborescent.

Basis membranous.

Mouth: labrum with only four very minute teeth: mandibles with four teeth; the third tooth broader than the first; the fourth small. Maxillæ, with the two upper spines placed on a slight prominence, beneath which there is a small notch. Cirri of a very dark colour (much injured): the segments of the first, second, and third pairs very broad and short, protuberant in front, and most thickly clothed with spines; the third pair is very little longer than the second pair: the sixth pair (in a large specimen above one inch in basal diameter) had the segments broader than long, each furnished with seven pairs of spines.

Affinities.—This species, though very distinct, evidently comes near to B. balanoides, especially to var. (a). By merely doubling or

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trebling the irregular rows of short tubes in the walls of B. balanoides, with their reticulated inner lamina and longitudinally folded outer lamina, we should have the structure exhibited in B. cariosus. We have seen, also, that in var. (a) of B. balanoides, the spur of the tergum is remarkably sharp, as in B. cariosus. This species, also, in a very marked manner approaches in many characters, especially in the opercular valves, in the cirri, and to a certain extent in the shell and basis, to B. flosculus, and even in external appearance to var. sordidus of the latter—an inhabitant of the opposite extremity of the continent, namely, of Tierra del Fuego. Again, the tergum to a certain extent, and the scutum in a singular manner, resemble these valves in B. nubilus, showing an unequivocal affinity to that species. With respect to the most remarkable character of the species, namely, the several irregular rows of tubes or pores in the walls, it deserves notice that in B. crenatus, which is certainly closely allied to B. balanoides, the longitudinal septa sometimes divide near the outer lamina, thus giving rise to a few additional tubes. Of the above several species, to which our present species is allied, B. flosculus stands in the next section, and B. nubilus and crenatus in the last: hence we see that B. cariosus has singularly divergent affinities. The peculiar structure of the parietes, together with the general appearance of the shell, made me at the first moment suppose I was examining a Tetraclita (or Conia of Leach); hence, also, it has arisen, that Lepas cariosa of Pallas has often been quite erroneously given as a synonym of Tetraclita porosa.

31. BALANUS DECLIVIS. Pl. 7, fig. 4 a-4 d.

Parietes solid; rostrum nearly twice as long as the carina or carino-lateral compartments, hence the basis is oblique. Tergum with the spur truncated, half as wide as the valve.

Hab.—West Indies; Mus. Brit.—Jamaica, imbedded in a sponge; Mus. Cuming.

This is a remarkable species; when first seeing it imbedded in numbers in a sponge, I did not in the least doubt but that it was an Acasta: on examination, however, it is found to have a membranous basis, and therefore cannot by the definition enter into that sub-genus, to which, however, it is very closely allied. It differs from other sessile cirripedes very remarkably in the rostrum being nearly twice as long as the carinal compartments, so that the basis is always very oblique, or placed almost on one side; in this elongation of the rostrum, although in a

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different direction, we are reminded of B. calceolus and its allies; and these latter we know can hardly be separated from certain species of Acasta. Hence the position of our present species in this section, is not natural; but I am unable to place it elsewhere, without breaking down every definition: it should stand somewhat isolated, on one side of a line of affinity connecting Balanus calceolus and navicula with Acasta purpurata.

General Appearance.—The shell is thin, fragile, smooth, and white, but covered to a considerable extent by a brown membrane, which on the sheath and opercular valve is of a bright tint, and clothed with bristles. Viewed laterally, the rostrum is seen to be considerably bowed, and from its being nearly twice as long as the other compartments, with its lower end bluntly pointed, the basal margin of the whole shell is rendered very oblique, forming a slightly concave line. The lateral compartments are rather longer, and about one third broader than the carino-lateral compartments. The rostrum, from terminating downwards in a blunt point, instead of being square or truncated, as in all other Cirripedes, and from the upper end being, as is usual, pointed, has, when disarticulated from the other compartments, the shape of a boat. The parietes are not at all porose: their internal surface sometimes shows traces of longitudinal ribs, but sometimes there are none. The radii are narrow, with their summits very oblique, and their sutural edges smooth. The sutural edges of the alæ are likewise smooth. The largest of Mr. Cuming's specimens was .2 of an inch in diameter; but a disarticulated specimen in the British Museum must have been larger, having a rostrum .3 in length. The Basis is membranous.

The Scuta are rather convex; they have their lines of growth approximate, most finely crenated, so as to be very feebly striated longitudinally. Internally, the articular ridge is pretty well developed, its lower edge being very oblique; there is barely an adductor ridge: the pit for the lateral depressor muscle is deep. The spur of the Tergum is placed close to the basi-scutal angle of the valve; it is about half as wide as the valve, with the lower end truncated: sometimes it may be rather said to be bluntly pointed, owing to its carinal side sloping up to the basal margin. The articular ridge is pretty well developed. The crests for the depressor muscles are barely discernible.

Animal's body unknown.

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Section F.

Parietes and radii not permeated by pores; basis sometimes permeated by pores, sometimes not permeated, sometimes excessively thin and hardly distinguishable.

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32. BALANUS HAMERI. Pl. 7, fig. 5 a-5 c.

LEPAS HAMERI Ascanius. Icones rerum naturalium, Tab. 10, 1767.

— TULIPA. O. F. Müller. Prodromus. Zoolog. Dan. 1776; sed non L. tulipa, in Poli, Test. ut. Siciliæ; necnon B. tulipa, in Bruguière, Encyclop, Method; necnon B. tulipa, in Sowerby, Genera of Shells.

— TULIPA ALBA. Chemnitz. Syst. Conch. Tab. 98, fig. 832.

— FOLIACEA. Spengler. Skrivter af Naturhist. Selskabet, 1 B. 1790.

BALANUS CANDIDUS. (Tab. emendata) Brown. Conch. Great Britain (1827), Tab. 6, figs. 9 and 10, et 2d edit. Tab. 54, figs. 9-12.

— TULIPA. Lyell.* In Phil. Transact., 1835, p. 37, Tab. 2, figs. 34-39

Shell white: radii with their oblique summits smooth and arched; sutural edges smooth: basis solid. Scutum feebly striated longitudinally: tergum with the spur narrow.

Hab.—Coast of Yorkshire; Scotland; Galway, Ireland; Isle of Man, and Anglesey, twelve fathoms. Generally in deep water; not very common. George's Bank, Massachussetts, United States; Mus. Aug. Gould. Iceland, Finmark, and the Faroe Island, according to Spengler. Attached to crustacea,

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* Sir C. Lyell remarks that this is apparently the B. Uddevallensis (Linn.) of Swedish lists of fossils. Prof. E. Forbes has shown (Mem. Geolog. Survey of England, vol. 1, p. 364) how this name arose, from a short description, prior to the introduction of the binomial system, "Lepas quæ Balanus Uddevallensis," given by Linnæus in his Wast-Gotha Resa, in 1747.

For the reference to Ascanius' work, which is on the binomial system, and subsequent to the 10th edit. of Linnæus, in 1758, I am greatly indebted to Mr. Sylvanus Hanley. Had it not been for this gentleman, I should have used Müller's name of B. tulipa as the first name.

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mollusca, stems of fuci, and stones; often associated with B. porcatus and crenatus.

Fossil.—In glacial deposits at Uddevalla in Sweden, and Beaufort in Canada; Mus. Lyell. Banks of the Dwina, Russia; Mus. Murchison. Greenland, "in blue clay," according to Spengler.

General Appearance.—Shell tubulo-conical, very smooth, white, generally more or less covered by yellow thin membrane; orifice large, sub-triangular: radii moderately broad, with their more or less oblique summits slightly rounded and smooth; from this circumstance the shell has been justly compared to the half-opened flower of a white tulip. Specimens often exceed an inch in basal diameter; I have seen one from Scarborough two inches in diameter and one and three quarters in height: another specimen was 1.6 in diameter and 3 in height. The specimens in the glacial deposits seem even to have acquired larger dimensions, one from Uddevalla being nearly four inches in height.

Scuta, elongated, flat, feebly striated longitudinally; internally, articular ridge short, moderately prominent: adductor ridge, confluent in the upper part with the articular ridge, running straight down and forming a rather large cavity for the lateral depressor. Terga feebly striated longitudinally, with a longitudinal furrow, having the sides, in old specimens, partly closed in: the basal margin slopes much towards the spur, which is rather long and narrow, with its end rounded: it is placed at about its own width from the basi-scutal angle. Internally, articular furrow narrow: crests for the depressores moderately prominent, but in a variable degree.

Compartments: these are unusually thin, and separate easily: the parietes are finely ribbed longitudinally on their insides; the bases of these ribs being just perceptibly denticulated. Radii, with their summits oblique (usually at about an angle of 45°), slightly arched and quite smooth: the smoothness is produced by the edge being a little inflected: sutural edge quite smooth, without even a trace of septa or denticuli. Alæ oblique, generally rather less oblique than the summits of the radii: sutural edges smooth, with an excessively fine linear furrow running along the edge, a little towards the inner side, and filled with a yellow ligamentous substance: a furrow of this kind I have seen in no other species.

Basis, solid, not permeated by pores; either smooth, or slightly furrowed in lines radiating from the centre.

Mouth: labrum with scarcely perceptible minute bead-like teeth thinly scattered along the edge. Palpi and outer maxillæ rather sparingly clothed with hairs. Mandibles with teeth rather sharp; the fourth and fifth teeth small, but well developed; inferior angle pointed with fine spines. Maxillæ with a deep notch under the two upper great spines. Cirri, the first pair is short, with rami of nearly equal length: the segments are not protuberant in front either in the first or second pairs. In the posterior cirri, the segments bear four pairs of spines, with a tuft of rather long intermediate spines: in young specimens there are only three pairs: the spines in the dorsal tufts are short and thin.

When the shell is disarticulated, this species cannot be confounded with any other; but judging by external characters alone, it may

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sometimes be very easily confounded with B. eburneus, and I have received the two species under this one name from Massachussetts: generally B. Hameri may be distinguished from B. eburneus by the smoothness of the summits of its radii, and by the so-called epidermis being of a darker yellow.

With respect to the fossil specimens from the glacial deposits, I have little to add; I have seen one from Uddevalla, as already remarked, four inches in height, and a lateral compartment broader by one fourth than the same compartment in any recent specimen. As Sir C. Lyell remarks (Phil. Transact.), the compartments are always found separated, which is accounted for by their weak union in a recent state. This species, when fossil, is usually associated with its deep-water congeners B. porcatus and crenatus, as at the present day.

I must here mention that I have examined a considerable number of separated compartments, without opercular valves, brought from Barbadoes, in the West Indies, showing the existence there of a closely allied or possibly identical species. The only difference which I can point out in these compartments is, that the parietes are rather thicker, and the radii rather narrower, with more oblique summits: some of the compartments are two inches in length. It seems very improbable that the true B. Hameri should extend to the West Indies, but after what has been seen in the case of B. crenatus, this is possible.

33. BALANUS AMARYLLIS. Pl. 7, fig. 6 a-6 c.

Shell striped or clouded with pinkish-purple, or quite white; radii narrow, with their oblique summits smooth or arched: basis porose. Scutum plainly striated longitudinally: tergum with the spur narrow.

Var. (a):* bright rosy pink, not distinctly banded longitudinally. Hab. North-east coast of Australia.

Var. (b): snow white, glossy; orifice deeply toothed.

Hab.—Mouth of the Indus; East Indian Archipelago; Philippine Archipelago; Moreton Bay, and the north-east coast of Australia. Attached frequently on ships' bottoms, associated with B. tintinnabulum and amphitrite. Sometimes attached to Gorgoniæ with B. calceolus.

General Appearance.—Shell steeply conical, with the orifice sub-rhomboidal, moderately large, very slightly, or deeply notched: surface very smooth: white, longitudinally banded with pinkish or leaden purple, with sometimes a purplish, sometimes a yellowish tint, the

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* This variety perhaps is the B. roseus of Lamarck, as figured in Chenu, "Illust. Conch." Tab. 2, fig. 9; but as Lamarck does not even notice such conspicuous external characters as the longitudinal striæ on the scuta, and the smooth rounded edges of the radii, it is impossible to identify his species.

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latter owing to the persistent epidermis; the bands are pale, and often fade away in the lower, and sometimes in other parts of the shell; the epidermis is generally more persistent on the narrow rounded radii than on the parietes, and hence the radii are generally yellowish. The opercular valves are pale dull purple: the sheath is darker purple, with the exception of the portions of the alæ added during the diametric growth, which are of a dead white, and are externally conspicuous. The scuta are striated longitudinally. I may remark, that, excepting the narrowness of the radii, with their quite smooth, rounded and very oblique summits, some specimens are hardly distinguishable, in external aspect, from varieties of B. amphitrite. If the specimens from the north-east coast of Australia, of which I have seen many (but unfortunately only one small one had its opercular valves), form, as I fully believe, merely a variety; it is characterised by its nearly uniform beautiful rosy pink, without any distinct longitudinal bands: of these specimens I have seen one two inches in basal diameter, and three in height: of ordinary duller-coloured striped specimens, the largest was 1.7 in basal diameter. Of the perfectly white var. (b), I have seen several specimens, the largest being .6 of an inch in diameter: these have a somewhat peculiar aspect, but I have met with only one specimen with opercular valves, and that was extremely young: I at first considered this form as specifically distinct; but I can point out, after careful examination of the whole shell, operculum, and internal animal of the young specimen, no sufficient diagnostic characters.

Scutum, plainly striated longitudinally, with the striæ dividing the prominent lines of growth into squarish beads: internally, the upper part of the valve is roughened: the articular ridge is short, remarkably little prominent, and not reflexed; the adductor ridge is blunt and little prominent: sometimes it is almost confluent with the articular ridge: there is a deep but variable depression for the lateral depressor muscle; and in young specimens of var. (a) it was almost absent. Tergum: the surface exhibits traces of longitudinal striæ: there is a deep longitudinal furrow, with the sides folded in and quite closed in full grown specimens: the scutal margin is considerably curved towards the scutum. The spur is long and narrow, with the end bluntly pointed, placed at rather above its own width from the basi-scutal angle; the basal margin slopes but little towards the spur: the crests for the depressores are feebly developed.

Parietes: their internal surfaces are strongly ribbed longitudinally, with the basal ends of the ribs coarsely denticulated, and with the denticuli extending close to the outer lamina. The radii are generally narrow, but their width varies; their summits are very oblique, smooth, rounded, and inflected, with the lines of growth, in the uppermost part, curving inwards; their sutural edges, in the upper inflected portion, are quite smooth, without septa; in the lower and larger portion, the edge is crenated with excessively fine teeth or septa, not denticulated: the radii, like the parietes, have no inner lamina: the recipient grooves in the opposed compartments are smooth, and are in the lower part of the shell of unusual depth. The alæ, differently from the radii, generally have their summits very slightly

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oblique, but sometimes they are highly oblique: their sutural edges are most finely crenated. The basis is generally flat, sometimes cup-formed; it is permeated by pores, crossed by transverse septa; and sometimes there is an underlying cancellated layer.

Mouth: labrum with either six very small teeth, or with none. Mandibles (Pl. 26, fig. 5), with the third tooth a little thicker than the first; fourth and fifth teeth small, but quite distinct. Maxillæ (Pl. 26, fig. 7), with the inferior part forming a square step-formed projection, bearing, one behind the other, two spines as long as the upper pair; in a young specimen of var. (a) this step-formed projection was absent.

Cirri: first pair with the rami unequal by about four segments: the shorter ramus has the segments very protuberant in front, thickly clothed with strongly serrated spines; the second cirrus has segments moderately produced; the third has them produced only in a slight degree. The pedicels of the second and third cirri have dorsal tufts of spines, but not a hairy plate prolonged over the thorax. The posterior cirri have segments broader than long, bearing only two pairs of nearly equally long spines; and between each pair there is a small intermediate tuft. The penis has the usual basi-dorsal point.

B. amaryllis is a distinct and well-defined species, more nearly related to B. Hameri than to any other form.

34. BALANUS ALLIUM. Pl. 7, fig. 7 a-7 d.

Shell faintly tinged with purple: radii broad, with their summits not oblique: basis not porose. Scutum with the lines of growth crenated: tergum with the spur extremely short, truncated, broad as half the valve.

Hab.—Raine's Islet, Barrier Reef, Australia, Mus. Stutchbury. Hab. unknown, attached to and coated by Porites. Mus. Brit.

General Appearance.—Shell conical, smooth, but with the lower part sometimes narrowly ribbed in lines corresponding with the internal longitudinal ribs; tinted pale peach-blossom purple, owing to the sheath being finely so coloured; or wholly white. Radii broad, white, square on the summit, hence orifice entire, ovate passing into rhomboidal. The parietal portion of the carino-lateral compartments extremely narrow, about one eighth of the width of the parietes of the lateral compartments. Basis concave, partially imbedded in the coral. Largest specimen .35 of an inch in diameter.

There are some specimens in Mr. Cuming's collection which appear to belong to this species, and are certainly very closely allied to it, but not having the opercula, cannot be identified positively; the shell is

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flatter, with the walls strongly ribbed up to the orifice, which is more rhomboidal: the basis is much more cup-formed and more deeply imbedded in the coral; but these differences by themselves are by no means sufficiently diagnostic.

Scutum: the lines of growth are crenated, causing the surface to be very obscurely striated longitudinally: the articular ridge is very prominent, as can be best seen from the outside, and runs down the whole length of the tergal margin with a very regular curve, and hence differs from the articular ridge in the foregoing species. The adductor ridge is either absent, or very indistinct, and parallel to the articular ridge: there is a deep little pit for the lateral depressor muscle. Tergum (7 d), with the apex somewhat produced or beaked, and tinged purple: external surface almost flat, without any longitudinal furrow: scutal margin curved. Spur very short, placed quite close to the basi-scutal angle of the valve; broad as half the valve; lower end square. Internally, the articular ridge is prominent only in the uppermost part of the valve: crests for the depressores very feeble.

Parietes: their internal surface is very strongly ribbed longitudinally, the ribs being coarsely denticulated at their bases, and finely fluted along their sides. The sheath is transversely ribbed, and clothed with an epidermis furnished with transverse rows of fine hairs. The radii are of a dead white, whereas the parietes are translucent; the summits are parallel to the basis; they are broad; the radii of the carino-lateral compartments appear extraordinarily broad, owing to the narrowness of the parietal portion: the sutural edges are furnished with coarse septa, which are sinuous, irregular, and obtusely denticulated; the interspaces are filled up solidly. The alæ are thin, with their sutural edges almost smooth, and their summits oblique: in some specimens, during the diametric growth, a mere, almost thread-like ribbon is added to their sutural edges. Basis slightly cup or saucer-shaped; moderately thick, permeated by fine pores, and generally ribbed in lines radiating from the centre. The walls and basis adhere together very firmly.

Mouth: labrum with six teeth: mandibles with five teeth; the three upper teeth being sharp, narrow, and unusually prominent; the two lower teeth minute and sharp; maxillæ without a notch. Cirri much injured: first pair with one ramus apparently one third longer than the other: segments not very protuberant: the posterior cirri have elongated segments with five pairs of spines.

Affinities.—This species is very distinct from all the foregoing: in the carino-lateral compartments being so narrow, and tending, as we may suppose, to become aborted; in the form and structure of the whole shell, and in its habits, this species shows an affinity and passage to the coral-inhabiting genus Creusia, which has only four compartments. There is also a close affinity to the sub-genus Acasta. This species is so closely allied to the following, that I at one time felt some doubts whether they ought to have been specifically separated: it is also probably closely allied to B. terebratus, but the materials hardly suffice for judgment: it is also related, though less obviously, to B. vestitus.

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35. BALANUS CEPA. Pl. 7, fig. 8 a-8 c.

Shell dirty reddish-purple, steeply conical: radii narrow: basis obscurely porose. Scutum with the lines of growth crenated: tergum with the spur truncated, broad as half the valve, and depending beneath the basi-scutal angle as much as half its own breadth.

Hab.—Japan, attached to an Isis, Mus. Cuming. Attached to an oyster, Mus. Stutchbury.

As already stated, this species comes in all essential respects very near to the last, though differing much in appearance; I have seen two sets of specimens, and two sets of B. allium, and there was no variability or passage in the points in which they differed; hence I must consider them as specifically distinct.

Shell, steeply conical, strongly but bluntly ribbed longitudinally; coloured either all over dull reddish purple, or with the upper part only pinkish purple: in one set of specimens, the yellow epidermis was partially persistent. Radii narrow. Orifice small, ovate. The wall of the carino-lateral compartment is very narrow. The internal surface of the parietes is ribbed, but finely, and only in the lower part. The septa, on the sutural edges of the radii, are finer than in B. allium. Basis flat, obscurely permeated by pores. The largest specimen is .25 of an inch in basal diameter.

Scuta: these are longitudinally and finely striated; the basi-tergal corner is more rounded off than in B. allium, and the articular ridge is not nearly so prominent: internally, the adductor ridge is rather more prominent. The Tergum is rather broader: its apex is produced into a minute sharp point: the scutal margin is straight; the spur is broader, and measured from the basi-scutal angle of the valve, considerably longer; namely, as long as half the width of the basal margin of the spur, whereas in B. allium it is only about a quarter as long as the basal margin of the spur: the lower edge of the spur is not here so directly transverse to the longitudinal axis of the valve as in B. allium: the external surface is not so flat as in that species, and a depression runs down to the basi-scutal angle of the spur.

Considering the difference in the shape and appearance of the shell, with its narrow radii and small orifice; considering the less strongly ribbed internal lamina of the parietes, the finer septa on the sutural edges of he radii, the slight

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difference in outline in the scuta and terga, more especially the greater length of the spur, I conceive I am right in ranking this form as a distinct species, though assuredly it is very closely allied to B. allium, and even still closer to the following B. quadrivittatus.

36. BALANUS QUADRIVITTATUS. Pl. 8, fig. 1.

Shell steeply conical, having four longitudinal gray bands placed crosswise: radii with their summits oblique: basis thin, solid. Scutum, with the lines of growth smooth; no distinct pit for the lateral depressor muscle: tergum as in B. cepa.

Hab.—East Indian Archipelago, attached to lamelliferous corals, and associated with Pyrgoma grande and Creusia spinulosa, Mus. Brit. and Stutchbury and Darwin. Philippine Archipelago, attached to a Tetraclita, Mus. Cuming.

I have seen four sets of specimens of this species, taken in four different places, one set containing above twenty individuals, and all resembled each other exactly: nevertheless, this species comes so close to B. cepa, that I am somewhat doubtful about it specific distinctness.

General Appearance.—Shell smooth, or slightly folded, steeply conical; white, with four longitudinal bands of pale brownish-gray colour, namely, on the rostrum, the carina, and the two lateral compartments: the carino-lateral compartments are very narrow and almost white: the four brownish-gray bands are darkest in the upper part of the shell, though always rather faint, and die out towards the base: they can sometimes be seen to be formed of several narrow longitudinal stripes; the tint shows a trace of containing purple. The orifice of the shell is small, rhomboidal, and not quite entire, owing to the obliquity of the summits of the moderately broad radii. In structure, the shell, radii, and alæ resemble those in the last species. The basis, however, does not appear to be permeated by pores. Basal diameter of largest specimen .25 of an inch.

The Scuta most closely resemble those of B. cepa, but the lines of growth are not crenated, and internally there is only a very minute pit for the lateral depressor muscle, placed almost on the edge itself of the valve. The Tergum hardly differs at all from that of B. cepa, but is perhaps of rather greater breadth.

The Mouth does not differ from that in the last two species. In the Cirri, the three posterior pairs have elongated segments, bearing only

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three pairs of spines, of which the lowest pair is minute: in B. allium, and I believe in B. cepa, there are five pairs of spines on each segment.

This species differs from the last only in the peculiar colouring, smoother walls, more oblique radii, solid basis, and more especially in the scuta having the lines of growth not crenated, and internally, in the pit for the lateral depressor muscle being so very minute and placed on the basi-tergal edge of the valve. The posterior cirri, also, I believe, differ in the number of the spines which the segments support; nevertheless, I cannot feel confident about the specific distinctness of B. quadrivittatus.

37. BALANUS TEREBRATUS. Pl. 8, fig. 2 a-2 b.

Shell white, strongly ribbed longitudinally, with the basal margin produced into long points: basis concave, not permeated by pores, but strongly ribbed externally in radiating lines; the interspaces between the ribs being riddled by minute rounded apertures, often placed in double rows.

Hab.—Unknown, Brit. Mus., attached to a lamelliferous coral.

I have in this instance broken through my rule of not describing a Cirripede without examining the opercular valves; but the species here named is so peculiar, that it would have been a fault to have passed it over. There is but a single specimen in the British Museum, without, as just stated, the operculum, and of course without the animal's body.

Shell, white, depressed, conical, somewhat elongated in its rostro-carinal axis; orifice rather small, pentagonal, toothed, elongated. Parietes rather thin, with extremely prominent longitudinal ribs, produced at the basal edge into long spikes: the internal surface is also ribbed, but less strongly than the outside. Radii rather narrow, with oblique, not smooth summits: sutural edges very finely and obscurely crenated. Alæ with their summits extremely oblique. Lower edge of sheath closely attached to the walls. The carino-lateral compartments are rather narrow.

Basis, slightly concave or saucer-shaped; the circumference is pro-

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duced into long spikes, corresponding with those on the basal margin of the parietes: these projections equal half the semi-diameter of the shell. The internal surface of the basis has slightly prominent, rounded ridges; and the external surface has extraordinarily prominent, sharp ridges, radiating from the centre; the edges of the external ridges are irregular, notched, and knobbed. I have seen in no other species external ridges on the basis or surface of attachment; and what is more remarkable, the interspaces between the ridges are penetrated by small rounded apertures, of irregular shape and unequal sizes; and these are generally arranged in an irregular double row, and externally are closed by the membrane, which clothes the basis. In the sub-genus Acasta, the basal cup is sometimes penetrated by similar holes, but these seem never to extend over the whole basis, and are very variable; nevertheless, in some specimens of Acasta spongites from the Cape of Good Hope, portions of the basis closely resembled, except in the absence of the radiating ridges, the structure here described, but the holes were not arranged in any definite order. The internal surface of the parietes in Acasta sporillus presents a somewhat analogous appearance, but the pits do not penetrate through the walls. This species, I have no doubt, is closely allied to the sub-genus Acasta, and to Balanus navicula with its allies, and, but much less closely, to B. allium with its allies. Indeed, had B. terebratus inhabited a sponge, I should have been compelled to have ranked it in the sub-genus Acasta.

38. BALANUS VESTITUS. Pl. 8, fig. 3 a-3 b.

Shell pinkish-purple or white, clothed by an orange-coloured membrane; radii represented by mere fissures: basis solid. Scutum, with a sharp, curved adductor ridge; with crests for the lateral depressor muscle: tergum, with the spur short, truncated, one third of width of valve.

Hab.—New Zealand, New South Wales, Mus. Brit. and Stutchbury; attached to shells.

General Appearance.—Shape conical, often steeply conical; orifice small; radii not developed, represented by mere fissures. The walls are smooth, or slightly, or strongly ribbed longitudinally. The shell itself is of a fine peach-blossom pink, or nearly white, but it is generally covered by a thick yellow or brownish-orange epidermis. Opercular valves pinkish, but similarly covered. Basal diameter of largest specimen .7 of an inch.

Scuta, with the lines of growth closely approximate; surface somewhat convex. Internally, the articular ridge is very little prominent, but runs far down the tergal margin; in some specimens, however, it is shorter and more prominent. The adductor ridge is strongly prominent, is curved towards the rostral angle, and runs down nearly to

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the basal margin. The rostral depressor muscle is lodged in a small cavity, formed, as usual, by the overlapping of the occludent margin; within this cavity there are either tolerably distinct little crests, or merely traces of them, for the attachment of the muscle. The lateral depressor muscle is attached to several quite distinct crests, seated in a concavity beneath the adductor ridge. Tergum rather narrow, with the apex produced or beaked: the beak is purplish and flat. There is a slight rounded longitudinal furrow, or depression. The spur is fully one third of the width of the valve: it is short, with the end truncated, and placed close to the basi-scutal angle; the basal margin on the carinal side slopes gently towards the spur. Internally, the scutal margin is scarcely at all inflected, and the articular ridge is very little prominent: the crests for the tergal depressors are pretty well developed.

From the points here enumerated, it is clear that the opercular valves are articulated together much less strongly than is usual with most species, excepting B. allium and its allies. It is remarkable that in this species the terga are united to the sheath, not, as is usual, by a single opercular membrane, but by five or six, one above the other, the upper membranes not having been exuviated as each new lower one was formed. The minute spines on the membrane lining the sheath are rather larger and more numerous than is usual, and to the base of each spine a tubulus of unusual diameter runs, imbedded in the shell.

The Walls, internally, have unusually numerous, narrow, approximate, strongly prominent, longitudinal ribs, denticulated at their bases, and inserted into the furrows on the borders of the basis: in old specimens these internal ribs die out in the upper part of the walls. The Radii are not developed in any of the many specimens which I have seen, and the edges of the compartments on both sides of each suture are equally marked by slight, irregular ridges or knobs, answering to the septa and their recipient furrows, in the species with ordinarily developed radii. There is very little diametric growth, the orifice being gradually enlarged by the disintegration of the upper ends of the walls; the alæ, however, in some specimens, do grow a little along their lateral or sutural edges, so that some little diametric growth must be effected. The summits of the alæ are very oblique; their sutural edges are plainly crenated. The sheath descends about half way down the walls. The Basis is flat, not permeated by pores, but deeply furrowed in lines radiating from the centre.

Mouth: labrum sometimes with no teeth, sometimes with four minute teeth; mandibles with four teeth, of which the third is blunt and rather large; the fourth is a mere knob. Maxillæ: there is, as usual, an upper pair of large spines (beneath which there is sometimes a small notch), but all the lower spines, instead of standing as usual in pairs, form a single row. Cirri; first pair with the rami remarkably unequal in length, one ramus having twenty-two segments, and being more than twice the length of the other, having only nine segments: these segments, and likewise those of the second and third pairs, have an inverted conical shape; and they are all less thickly clothed with spines than is usual. The second pair is short, about as long as the

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shorter ramus of the first pair, and has ten or twelve segments. The third pair is above twice as long as the second pair, and contains twenty-four segments: this very unusual length is owing to the presence of numerous thin tapering upper segments, unlike those generally found in Balanus, in the third pair of cirri, and apparently serving as feelers. These upper tapering segments are of an inverted conical shape, and support on their upper margins two very small tufts of spines, one behind and one in front: on the segments lower down these tufts increase in size, and the spines are more spread out, so that in the basal segments, the tufts in front form on the upper margin two or three crowded rows of bristles. The three posterior pairs of cirri have elongated segments, which bear on their upper half three pairs of spines; of these the lowest pair is minute, and the middle pair is only one third of the length of the upper pair. The sixth cirrus, in the same individual as before, contained twenty-seven segments in each ramus, that is only three more than in the third cirrus! I must observe, that the cirri in all the specimens were irregular, often distorted and monstrous; and therefore, probably, there is considerable variation in the proportional numbers of the segments in the cirri.

At the base of the penis there is a minute, knife-edged, triangular projection. The branchiæ are rather narrow, pointed, and not very large.

Affinities.—This is a very distinct species, as shown by the peculiarities in the cirri, by the absence of radii to the shell, and by the presence of crests for the attachment of the lateral scutal depressores. With the exception of this latter character, the opercular valves clearly show, that B. vestitus is allied to B. allium, cepa, and quadrivittatus. In some respects this species manifests an affinity to B. imperator, which latter has its third pair of cirri nearly similar to those of B. vestitus.

39. BALANUS IMPERATOR. Pl. 8, fig. 4 a-4 c.

Shell internally imperial purple; parietes thick, with their internal basal edges rough with irregular points and ridges; radii narrow; basis very thin, solid. Scutum, with crests for the rostral and lateral depressor muscles: tergum, with the end of spur rounded.

Hab.—New South Wales, Sydney, Port Stephens, Moreton Bay; attached to sandstone-rocks and shells, at low-water line; Mus. Brit., College of Surgeons, Cuming, Stutchbury.

Shell conical, very thick and very strong; longitudinally sulcated more or less strongly; whole thickness of shell beautifully coloured rich violet, or more strictly "imperial purple"; externally the surface, from disintegration, is generally whitish; internally the colour is best developed: the narrow radii and the thin basis are white. The largest

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specimen which I have seen was one and three-quarters of an inch in basal diameter, the walls close to the basis being, in this instance, actually .3 of an inch in thickness.

Operculum thick and strong, covered by yellowish-brown epidermis; internally, the shelly substance is either all of the richest purple or yellowish-white, tinged, especially in the upper part, with purple. Scuta, with the apex beaked and somewhat reflexed; articular ridge very thick, little prominent: articular furrow very narrow, the impression made by the adductor muscle is seated very high up the valve; there is hardly an adductor ridge, but the surface of the valve is angularly prominent in a curved line, running from the articular ridge to near the rostral angle of the valve. At the rostral angle, the occludent margin is not folded inwards, as is generally the case, but the surface is flat, and is marked by four or five crests for the attachment of the rostral depressor muscle. There are other crests for the lateral depressor muscle. Tergum, with the apex somewhat produced and beaked, but blunt; longitudinal furrow shallow; spur of moderate breadth, with its lower end rounded; the basal margin on the carinal side of the spur slopes towards it. Internally, articular ridge moderately prominent. Crests for the tergal depressor well developed.

Parietes, solid, thick, with the basal internal edge (4 c) formed of short ridges, or flattened and irregular points, which in very old specimens are but little prominent; inner surface, finely, closely, and irregularly ribbed longitudinally, but in some specimens nearly smooth. The radii are nearly white; they are narrow, sometimes hardly at all developed, and have their summits very oblique and jagged; exteriorly, they are sulcated in a transverse direction, and sometimes form oblique steps, from having been formed layer over layer: their sutural edges are formed of irregularly branching crests or septa. The alæ have their summits very oblique; their sutural edges are thick and crenated: the part added during diametric growth on the inner surface is smooth, and has a different appearance from the transversely ribbed portions of the sheath, of which the alæ form a portion. The lower edge of the sheath is hollow beneath. The carino-lateral compartments are very narrow.

Basis calcareous, thin, white, sometimes opalescent, apparently formed by an aggregation of very minute calcareous beads, with no trace of furrows radiating from the centre.

Mouth: labrum hairy, with apparently some very minute teeth; mandibles, with the fourth and fifth teeth small and rudimentary; maxillæ rather broad, with a narrow and rather deep notch under the two great upper spines: outer maxillæ with the lower lobe very large.

Cirri: First pair, with the rami unequal by several segments: second pair, with the rami unequal in length by about six segments: third pair elongated, with the segments very numerous, almost equalling those in the sixth cirrus; upper segments of both rami much elongated, each with only a circle of spines; segments in the above first three pairs of cirri only slightly protuberant. Posterior cirri elongated, with the upper segments bearing three pairs, and the lower segments four pairs of main spines, between which there is a small intermediate tuft.

19                          

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Affinities.—This noble Balanus, in all the characters derived from its opercular valves, and from its cirri, is closely allied to the last species: in the structure, however, of the shell and of the basis, it comes closer to the following, B. flosculus. The crests on the under side of the scutum, for the lateral depressores, are confined to these three species; and the crests for the rostral depressores are confined to B. imperator and vestitus, but they are generally rudimentary in the latter: The internal basal structure of the parietes is singularly like that of Chelonobia caretta, though there is no other special affinity to that genus. In the nature of basis; in the structure, to a certain limited extent, of the walls of the shell; in the narrowness of the carino-lateral compartments; in the elongation of the third pair of cirri; in the crests for the rostral and lateral scutal depressores, B. imperator comes nearer to the genus Tetraclita than does any other species of Balanus.

40. BALANUS FLOSCULUS. Pl. 8, fig. 5 a-5 f.

Shell purple or dirty white, with the internal basal edges of the parietes rough with irregular points and ridges; radii narrow or absent; basis excessively thin, in appearance absent. Scutum with crests for the lateral depressor muscle: tergum very narrow, with the spur pointed.

Var. sordidus. (Pl. 8, fig. 5 b) shell globulo-conical, dirty white, with numerous sharp, narrow, longitudinal folds or ridges.

Hab.—Peru and Chile; generally attached to the Concholepas Peruviana, or to Balanus psittacus, and associated with Chthamalus scabrosus. Var. sordidus, inhabits Tierra del Fuego, attached to littoral shells, wood, and rock, associated with Ch. scabrosus.

General Appearance.—Shell either extremely much depressed and irregular, or globulo-conical, or more rarely cylindrical and elongated. Walls, either with a few rather broad, smooth, irregular, longitudinal folds, or, in var. sordidus, with numerous sharper and more prominent longitudinal ridges; basal margin very sinuous. Colour, either fine rich peach-blossom purple, or so pale as to be almost white; or in var. sordidus dirty white, generally stained greenish from confervoid matter. Orifice small, oval, entire. Radii very narrow, white, or not at all developed, and with even the sutures not distinguishable. The purple coloured varieties, with the narrow white radii, the small oval orifice, and folded walls, have a very pretty appearance, which is far from the case with var. sordidus. The largest specimens attained a basal diameter of .6 of an inch, but this is an unusual size: I have seen a cylindrical specimen of var. sordidus one inch in length.

The opercular valves are united to the sheath by unusually strong membrane: internally, their upper parts are stained purple. Scuta, these vary considerably in breadth, some being even broader than in

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Pl. 8, fig. 5 c, and others as much elongated as in fig. 5 d: these latter come from an elongated cylindrical shell. The valve externally is unusually convex: the apex, also, projects freely to an unusual degree. Internally, the articular ridge is moderately prominent: the adductor ridge is prominent and much curved: in the upper part it either lies close to, or at some little distance from the articular ridge. The lateral depressores are attached to several little crests, occupying a cavity, (often bordered above by a little ridge) close beneath the adductor ridge. Tergum, extraordinarily narrow and elongated; beak triangular, purple: a longitudinal furrow runs down the valve: spur narrow, long, bluntly pointed, lying close to the basi-scutal angle of the valve: the scutal margin is nearly straight and parallel to the spur. Internally, the articular ridge is prominent: the crests for the depressores are moderately well developed: the upper part of the valve is marked by a purple patch, bounded on one side by the articular ridge, and on the other side by a very slight special ridge. There is some variability in the narrowness of the whole valve, and in the sharpness of the spur.

Parietes.—The under surface, in the more depressed varieties, is roughened in a remarkable manner nearly or quite up to the sheath, with very irregular, projecting, and branching ridges, and sometimes with depending points. These ridges and points are granulated on their under surfaces. The roughened surface in the more conical varieties is confined to the basal inner margin. This structure is nearly the same as that in B. imperator, represented (Pl. 8, fig. 4 c), but the little ridges are here more apt to be concentric, instead of radiating. The lateral edges of the compartments on the inside, especially the carinal edges, project inwards beyond the inner surface of the shell. The sheath is but little hollow on its under side. The diametric growth of the shell seems to be quite capricious: in the same group, some individuals thus increasing, and others not at all. When the radii are developed they are narrow and white, with their upper margins nearly if not quite parallel to the basis: their sutural edges are formed by large, irregular, branching teeth or septa. The alæ, also, have their sutural edges coarsely crenated; and when the shell increases by diametric growth, they are added to above the opercular membrane, so as to be nearly square at top.

Basis.—When a shell is removed from the surface of attachment, and inspected even under a lens, there appears to be no basis whatever, either adhering to the shell, or to the supporting surface: but when a more careful examination is made, with a higher power, an excessively thin, translucent, calcareous, irregular layer, or rather film, can almost always be discovered. This would be more easily distinguished if the specimens had adhered to rock instead of to the rugged shells of molluscs. At one time I thought the basis was partially membranous, for I have certainly scraped off small fragments of membrane from the supporting surface; but these, when examined under the compound microscope, seemed always to consist of a thin sheet of the yellow cementing tissue; and in some instances, a brittle film of shell, representing the true basis of the cirripede, still adhered to the upper surface of the membranous bits of cement. Nevertheless, so imperfect is the

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calcareous basis, that I should not be surprised if portions of a true membranous basis did really in some cases exist.

Mouth: labrum with the notch wide, generally with a few little teeth; mandibles with three teeth, and some inferior knobs: maxillæ notched. Cirri, first pair with one ramus shorter by three segments than the other ramus. Second and third pairs short, of nearly equal length, thickly clothed with spines; segments very little protuberant. Posterior cirri, having elongated segments, supporting seven pairs of spines.

Var. sordidus.—This form is very common on the tidal shores of the Strait of Magellan, and of the southernmost parts of Tierra del Fuego, near Cape Horn: it lives attached to rocks, mytili, and logs of wood, and is associated with Chthamalus scabrosus. It almost certainly is the most antarctic form of the genus Balanus. If I were guided by external appearance alone, I should certainly separate this form specifically from B. flosculus, but, as will be seen in the following description, the differences consist only in var. sordidus being much duller and rather differently coloured, in the longitudinal folds being sharper and more prominent, and in the whole shell being rather more globular, and on an average rather larger; but in the true B. flosculus there is considerable variation in all these respects, as there likewise is in var. sordidus; thus some of the cylindrical varieties of the latter have less prominent ridges than even var. flosculus. In general appearance I have seen some nearly, but not exactly, intermediate forms; therefore, I do not feel positive that these forms may not be specifically distinct, but have failed, after careful examination, to find any sufficient diagnostic characters. Moreover, in the case of Balanus lævis, I was led to believe that there is an equal and somewhat analogous amount of variation in the specimens inhabiting Tierra del Fuego and northern Chile; and in this case I was enabled to show the existence of strictly intermediate forms in the intermediate districts.

The shell in var. sordidus is generally globulo-conical, dirty white, frequently with a green tinge, from the growth of confervoid matter. Orifice small. The exterior surface is covered with numerous prominent, narrow, sharp ribs or folds, the basal margin being serrated with projecting points where the folds terminate. When the radii are not developed, the sutures are very often obscure. Internally, the shell is faintly tinted of a port-wine purple. In all points of structure this form is identical with the true B. flosculus. In some few specimens the whole exterior surface was disintegrated and smooth; and this is generally the case with the upper parts of the shell. Some other specimens, which had grown crowded together on wood, had become cylindrical, and consequently the orifice was as large in diameter as the shell, namely, half an inch: in some of these cylindrical varieties the sheath was entirely soldered to the walls. The largest specimens which I have seen were .6 of an inch in diameter; and above one inch in height.

Affinities.—This species, in its opercular valves, even in such trifling characters as the strength of the opercular membrane, and in its cirri, approaches closely to B. cariosus. We even see on the under side of

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the scutum, in that species, a single little ridge, foreshadowing, as it were, the crests for the lateral scutal depressores, so remarkable in our present species. In the structure of the shell and of the basis, B. flosculus is much more closely related to the last species, or B. imperator. If it had been possible to have arranged the species in a single line, B. flosculus ought undoubtedly to have been placed between B. cariosus and imperator.

41. BALANUS BISULCATUS. Pl. 8, fig. 6 a-6 c.

BALANUS SULCATINUS. (?) Nyst, apud D'Omalius (sine descript. aut tabulâ), Geologie de Belgique, 1853.*

Radii with their upper margins oblique and smooth; sutural edges smooth: basis permeated by large pores. Scutum narrow, with from two to four longitudinal furrows: tergum with the spur very short, broad as half the valve.

Var. plicatus, with the walls deeply folded; radii narrow, with their upper margins very oblique.

Fossil in Coralline Crag, Ramsholt, Gedgrave, Sutton; Mus. S. Wood, Bowerbank, J. de C. Sowerby. Rauville, dans le Cotantin, Mus. G. B. Sowerby. Var. plicatus, Coralline Crag, Sutton, Mus. S. Wood. Bolderberg, near Hasselt, Belgium, Mus. Bosquet.

General Appearance.—Shell conical or tubulo-conical, often rather globose; walls frequently thin, either very smooth, or deeply plicated longitudinally: occasionally the same specimen is smooth in the upper part, and strongly plicated in the lower. The Radii in the larger specimens are wide, and with their upper margins only slightly oblique; in the smaller, they are narrower and much more oblique, but in each case their upper margins are smooth and slightly bowed. Colour apparently originally nearly white, but with the alæ generally, in the smaller specimens, clouded with a dark tint: the radii are usually striped feebly in longitudinal lines. Basal diameter of largest specimen .8 of an inch; but this seems to have been an unusual size.

Scuta: narrow, with the basal margin forming an unusually small angle with the occludent margin; surface slightly convex, with lines

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* I am indebted to M. Bosquet for a specimen, bearing this name and reference, found in the 'Systeme Bolderien' of Dumont, (miocene according to Sir C. Lyell) at Bolderberg. The specimen consists of a rostrum, with a portion of the base attached; and as these parts are in some degree characteristic, I fully believe this specimen to be the B. bisulcatus. I hope hereafter to give in the Palæontographical Series fuller illustrations of this and the following fossil species.

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of growth approximate, moderately prominent; on the tergal half of the valve, two distinct rather broad furrows, with sometimes a third, and even a fourth, nearer to the occludent margin (Pl. 8, fig. 6 a), extend from the apex down the valve, and give it a very peculiar appearance: the furrows near the tergal margin are the deepest. Internally, the upper part of the valve is roughened with small points: the articular furrow is unusually wide: the articular ridge is very prominent and but little reflexed, with the lower end almost abruptly cut off: the adductor ridge is prominent, but short: there are small deepish pits for the rostral and lateral depressores.

Terga (6 b), broad, flat, with a slight narrow prominent rim along the scutal margin, which margin is slightly bowed. The basal margin on the carinal side of the spur slopes so gradually towards the spur, that the latter is barely distinct, and is very short, not depending nearly half its own width beneath the basi-scutal angle: it is broad, namely, measured across the upper part, as broad as half the valve; its basal end is obliquely rounded off on the carinal side; it is placed close to the basi-scutal angle. The carinal margin of the valve is just perceptibly bowed, and is formed by rectangularly upturned lines of growth. Internally, the upper part of the valve is rough; the articular ridge is prominent; the crests for the tergal depressores muscles are moderately well-developed.

Parietes, not porose; internally, the ribs are smooth, with their basal edges very finely or barely denticulated. The radii (as already stated) are of variable breadth; they have their upper margins either very slightly or highly oblique, but always smooth and rounded: their sutural edges are quite smooth, or sometimes, with a strong lens, traces of transverse striæ, representing septa, can just be discovered. The alæ have their upper margins very oblique; their sutural edges are, in the large specimens, quite smooth; in the younger ones, plainly crenated; the recipient furrow being clearly marked with these teeth. Basis plainly porose.

Varieties.—It is certain that there are longitudinally plicated specimens of this species, and that the obliquity of the upper margins of the radii also varies a little: nevertheless some of the deeply plicated specimens undoubtedly have a very different aspect from the ordinary varieties, and do really differ in the sutural edges of the alæ being crenated, and in the greater narrowness and obliquity of the radii; but these points are all commonly variable. I have not seen any large specimens of the variety, plicatus, so as to compare them with the large specimens of the normal form, yet I can hardly entertain any doubt, considering their agreement in so many important points, that I have rightly treated these forms as mere varieties; it is unfortunate that none of the specimens of the var. plicatus seen by me have had opercular valves, as their presence would have removed all shadow of doubt.

Affinities: this is a strongly characterised species, and nearly allied only to the following species, B. dolosus. The furrows on the scuta in some degree resemble those on B. lævis, but there is no alliance with that species. It is certain that amongst recent species, the chief affinity is with B. Hameri and amaryllis.

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42. BALANUS DOLOSUS. Pl. 8, fig. 7.

Radii with their upper margins oblique and smooth; sutural edges smooth: basis permeated by large pores. Tergum with the spur not very short, broad as one third of valve.

Fossil in Red and Mammaliferous Crag, England; Mus. S. Wood, Bowerbank, Lyell, J. de C. Sowerby, Henslow, &c. Mammaliferous Crag, Postwick, near Norwich, Mus. Lyell.

This species so closely resembles B. bisulcatus, both externally and in all the essential characters of the parietes, radii, and basis, that it is quite superfluous to describe over again these parts. The specific characters are derived from the opercular valves, which present well defined distinctions, found by me constant in several specimens of both species. B. dolosus, like B. bisulcatus, has quite smooth and deeply plicated varieties, often adhering to the same univalve. The ribs on the inner surfaces of the parietes are remarkably prominent. I think the upper margins of the radii are in this species rather more oblique than in B. bisulcatus. The sutural edges of the radii are marked by the finest striæ, representing septa. The sutural edges of the alæ are generally distinctly crenated. The basis is often slightly cup-formed, and very plainly porose: its surface is marked by radiating ridges. The orifice of the shell is large, and elongated, especially in young specimens. The basal diameter of the largest specimen is .4 of an inch.

The Scuta have no trace of the two or three longitudinal furrows so conspicuous on these valves in B. bisulcatus, and which, in that species, run down from the apex of the valve; this fact showing that the furrows occur in quite young individuals. The whole valve is not quite so narrow as in B. bisulcatus, but otherwise agrees with it in shape: internally, there is hardly any difference: the articular furrow is not so wide: the articular ridge is very prominent, and abruptly truncated at its lower end: the adductor ridge is also prominent; it here runs a little higher up the valve than in B. bisulcatus. The Tergum differs more in the two species: the spur is not so broad; measured in its upper part, it is only about one third of the entire width of the valve, instead of being

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half as wide as the valve: it is considerably longer, depending beneath the basi-scutal angle more than half its own width: the basal margin of the valve on the carinal side, does not slope so gradually into the spur: the occludent and carinal margins are slightly arched, as in B. bisulcatus. Internally, the surface is rough, the articular ridge is prominent, and the crests for the tergal depressores are well developed,—all as in B. bisulcatus. It is remarkable, how generally the opercular valves have been preserved in this species in its fossil condition, as compared with most other species of the genus.

It is not easy to distinguish by external characters the rugged varieties of this species from B. crenatus; indeed, the only difference is that the furrows receiving the edges of the radii, generally, exhibit in B. crenatus a slight impression of the septa, which are entirely absent in B. dolosus. By internal characters, such as the non-porose parietes, and porose basis, our present species widely differs from B. crenatus.

43. BALANUS UNGUIFORMIS. Pl. 8, fig. 8 a-8 b.

BALANUS UNGUIFORMIS. J. de C. Sowerby (!) Mineral Conchology (sine descriptione) Tab. 648, fig. 1, (Jan. 1846).

— ERISMA. J. de C. Sowerby (!) Ib., fig. 2.

— PERPLEXUS. Nyst, apud D'Omalius (Sine descript. vel Tab.), Geologie de la Belgique, 1853.*

Parietes thin, sometimes permeated by pores; radii with their upper margins oblique; sutural edges very finely crenated: basis solid. Tergum with the spur narrow, bluntly pointed.

Var. erisma, with the walls longitudinally folded or ribbed.

Fossil in the Eocene formation, Isle of Wight, Colwell Bay; Hordwell; Barton, (Chama Bed); Headon: Bembridge. Bergh, near Klein Spauwen, Belgium (?). Attached to various shells and wood. Mus. J. de C. Sowerby, E. Forbes, F. Edwards, Charlsworth, T. Wright, Bowerbank, Tennant, Bosquet.

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* I am much indebted to M. Bosquet for specimens bearing this title, from Klein Spauwen, which certainly appear to me, as far as can be judged by the separated compartments, without the opercular valves, to belong to our present species.

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This species, the most ancient one as yet well known in the genus, presents to the systematist a most unfortunate peculiarity, in the parietes being almost as often as not permeated by small pores: I have seen no other instance, except to a limited degree in B. glandula, of this character being variable, and hence it must be still considered of high classificatory value, in so varying genus as Balanus. Owing to this varying condition of the parietes, together with the basis being quite solid, our present species has as good a claim to be ranked in the last as in the present section; indeed, I think it has more affinity to B. crenatus and glandula in the last section, than to any other recent forms: I have placed it in its present place, owing to its intimate affinity to B. varians, in which the parietes seem always to be solid; and partly, I believe, because all the first specimens examined by me exhibited no traces of parietal pores. Owing to the kindness of Mr. F. Edwards, I have seen the original specimens, excellently figured by Mr. J. de C. Sowerby in the 'Mineral Conchology:' I can perceive no difference between B. unguiformis and erisma, excepting that the walls in the latter are longitudinally folded,—a character we know to be variable in so many species. In both varieties, the parietes are sometimes porose and sometimes solid. The smaller specimens, however, figured in the 'Mineral Conchology' to the right hand, may possibly be a distinct species, as I infer from the narrowness of their radii.

General Appearance.—Shell, tubulo-conical, sometimes considerably elongated and sub-cylindrical: surface either very smooth, or slightly folded, or deeply folded so as be strongly ribbed longitudinally: orifice rather large, rhomboidal, narrow at the carinal end, toothed, but not deeply: walls rather thin and fragile: radii of moderate width, with their summits oblique, not quite smooth. Basal diameter of largest specimen, about three quarters of an inch.

Scuta, with the external surface smooth: there is a trace of a furrow running down the valve from the apex, near to the occludent margin, and this is only worth mentioning from the analogous furrows in B. bisulcatus. Internally, the upper surface of the valve is roughened: the articular ridge is very prominent, and slightly reflexed: there is no distinct adductor ridge; there is a slight but variable depression for the lateral depressor. Tergum, with the longitudinal furrow shallow; spur moderately long, about one fourth or one fifth of the width of the

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valve; placed at about its own width from the basi-scutal angle; basal end bluntly pointed; the basal margin on the opposite sides of the spur forms a nearly straight line; the carinal margin has an extremely narrow border formed by upturned lines of growth. Internally, the surface is roughened with little points: the articular ridge is prominent: the crests for the tergal depressores moderately prominent.

Parietes: the longitudinal ribs on the internal surface are either feebly, or, in the lower part, strongly developed; their basal ends are only just perceptibly denticulated. As already stated, in about half the specimens, there were no traces of parietal pores; in the other half there were either distinct or obscure pores; the pores are circular, generally of unequal sizes, and never large; in the same individual they would sometimes be almost wholly absent in some of the compartments, and quite plain in the other compartments. The Radii are either moderately wide or rather narrow, and have their upper margins very oblique, and not distinctly arched, and not quite smooth: their sutural edges are very finely crenated, the teeth or septa not being denticulated. The upper margins of the alæ are rather less oblique than those of the radii: their sutural edges are barely crenated. The basis is thin, and without any trace of pores; the upper surface is sometimes furrowed in radiating lines.

44. BALANUS VARIANS. Pl. 8, fig. 9.

B. VARIANS. G. B. Sowerby, in Darwin's Geolog. Observ. on South America, (Sept. 1846), Tab. 2, fig. 4, 5, 6.

Parietes moderately thick: radii with their upper margins very oblique; sutural edges almost smooth, or finely crenated: basis finely porose. Tergum with the spur small, narrow, bluntly pointed.

Hab.—Port St. Julians, Patagonia; ancient Tertiary formation. Eastern plain of Tierra del Fuego (?)

This species comes so close to B. unguiformis, that I have some doubt whether they ought to be specifically separated: the whole shell is stronger, and the basis can be seen to be porose when a polished section is made: the spur of the tergum is smaller, more pointed and more medial, but these latter differences may be due to mere variation. Should B. varians and unguiformis prove to be the same species, the latter name has the priority.

General Appearance.—Shell moderately strong and thick; shape conical or tubular, or even inverted conical; orifice moderately

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toothed, large, sub-trigonal; walls either smooth or longitudinally folded; the elongated specimens are most apt to be smooth. The Radii are narrow and oblique. Diameter of largest specimen above three-quarters of an inch.

Scuta, with the lines of growth moderately prominent; the internal surface of the valve has been ill preserved; but a very prominent, hardly reflexed, articular ridge, can be distinguished, as well as the absence of an adductor ridge. Terga, with no distinct longitudinal furrow running down the valve: spur short, bluntly pointed, narrow, about one fifth or one sixth of width of valve; placed at above its own with from the basi-scutal angle; the basal margin, on each side close to the spur, curves towards it. Internally, all that can be distinguished, is that the articular ridge is prominent.

Parietes; their inner surfaces appear to have been nearly smooth; the absence of parietal pores could be made out only by polishing a transverse section. The Radii are narrow, and have their upper margins very oblique and rather smooth: in the elongated varieties the sutural edge appears to be almost absolutely smooth; in the conical specimens it is slightly crenated, the septa being apparently not denticulated. In living species we have a similar variation in the state of the sutural edges of the radii, in B. balanoides and crenatus the edges being much smoother in much elongated specimens than in other varieties. The alæ have their upper margins less oblique than those of the radii, with their sutural edges barely crenated. The Basis is either flat, or, in the elongated specimens, deeply cup-formed; in section it can be seen to be finely and irregularly porose.

45. BALANUS INCLUSUS. Pl. 8, fig. 10 a-10 c.

Shell reddish-brown: radii broad, with their upper margins not oblique, or only moderately oblique; sutural edges with plainly denticulated septa: basis porose. Scutum without an adductor ridge; tergum with the spur rather narrow.

Var. (a) (Pl. 8, fig. 10 b, 10 c), with the shell elongated in its rostro-carinal axis; basis narrow, clasping the stem of a zoophyte; lateral compartments much broader than the almost linear rostrum, carina, and carino-lateral compartments.

Var. (b), with rough longitudinally folded walls, and with the summits of the radii forming an angle of about 45° with the basis.

Fossil in Coralline Crag, Sutton and Gedgrave; attached to foliaceous Bryozoa; Mus. S. Wood, Bowerbank. Var. a. Coralline Crag, Sutton, attached to cylindrical branches of corals; Mus. S. Wood. Var. b. attached to shells, Osnabruck, Hanover, Mus. Lyell; Bünde, Westphalia, Mus. Krantz.

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My materials consist of a beautiful series of specimens in Messrs. Wood and Bowerbank's collections; but unfortunately only a single young specimen had its opercular valves preserved. Not one specimen of the very curious variety (a) had opercular valves, yet I cannot feel any doubt about its being only a variety, caused by its attachment to a thin cylindrical branch of a coral, instead of to a foliaceous Bryozoon; it will, however, be convenient to give a separate description of this very remarkable form. With respect to var. (b), both sets of specimens came to me with the name B. stellaris, of Bronn; but as Bronn distinctly states, that in his species the parietes are porose, and as such is not here the case, this cannot possibly be that species: these specimens did not possess their opercular valves, and therefore cannot be identified with certainty.

General Appearance.—Shell conical, with the orifice rather large, and rhomboidal. The surface is very smooth, except in var. (b.) from the Continent, in which it is rugged and longitudinally folded. The colour is ochreous-brown (chiefly no doubt derived from the imbedding substance) tinged with red. The radii often have a much darker and more distinct red tint; they are sometimes longitudinally striped with dirty white. The radii are broad, with their summits straight, and very slightly oblique; in var. b, however, they slope at an angle of about 45°. Basal diameter of largest specimens .6 of an inch; but this is an unusual size.

Scuta (from a young individual), with the growth ridges little prominent. Internally the articular ridge is moderately prominent, with its lower end very obliquely rounded off; there is no adductor ridge; there is a minute pit for the lateral depressor muscle. Terga, with a slight longitudinal depression extending down to the spur: spur short, with its lower end almost square or truncated, about one fourth of width of valve, and placed at about half its own width from the basi-scutal angle. Internally, the articular ridge is prominent; the crests for the tergal depressores are feebly developed.

Parietes, moderately thick and generally strongly ribbed internally, without parieted pores. Radii, wide, with their upper margins straight, not smooth or rounded, and very slightly (or, in var. b, moderately) oblique; their sutural edges have well-developed septa, which are denticulated: the interspaces between the septa are filled up solidly. The alæ have their upper margins oblique: they are only slightly and sometimes not at all, added to above the level of the opercular membrane: their sutural edges are smooth. The basis is thin, but plainly porose.

Var. (a).—With respect to this remarkable variety, any one would at first think it specifically distinct. The shell is much compressed, or elon-

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gated in the rostro-carinal axis, sometimes to a great degree; I have seen a specimen .25 of an inch in this axis and only .1 in its broadest part; but this is a very unusual degree of elongation. The most remarkable character is the extraordinary narrowness of the carina, the carino-lateral compartments, and of the rostrum, compared with the great breadth, especially along the basal margin (Pl. 8, fig. 10 b, 10 c), of the lateral compartments. The radii are of unusual breadth. The tips of the rostrum and of the lateral compartments are a little arched in, tending to make the shell somewhat globular. The true basis is extremely narrow (fig. 10 c): it is deeply grooved, from clasping the thin, cylindrical stem of the coral to which it had adhered; and I have seen specimens in which the opposite edges of the groove had met, a tube having been thus actually formed. From the grooved basis, and from the elongation of the shell in the rostro-carinal axis, this species presents so close a general resemblance to Balanus calceolus, and its allies, that I have seen it in a collection arranged on the same tablet with a fossil specimen of B. calceolus. Notwithstanding the above several strongly-marked characters, by which this variety differs from the ordinary form, there is a resemblance in colour and aspect, which though difficult to be described, made me from the first suspect that the two were specifically identical. In no point of real structure is there any difference, excepting that, perhaps, the pores in the basis are here rather smaller; but this might arise from the little development of the peculiar basis. Having come to this conclusion, I was interested by finding a specimen in Mr. Wood's collection, which had originally fixed itself (judging from the form of the basis) on a cylindrical stem, but which had subsequently grown on to an adjoining flat surface; consequently, one side of the shell presented all the peculiar characters of the present variety, whereas the other side, at the rostral end, was undistinguishable from the ordinary form. The unequal development of the rostrum on the two sides was very striking, and clearly showed how great an effect could be produced by the nature of the surface of attachment.

This singular variety cannot be considered accidental, in the sense in which this term may be applied to some varieties: the larva evidently fixes itself intentionally, in a certain definite position, on the branch of the coral (when a branch is chosen), exactly as in the case of Balanus calceolus, or Scalpellum vulgare. But when other species of Balani occasionally fix themselves on branched corals, their position seems to be accidental and unsymmetrical; thus among the symmetrically elongated specimens of the present species, I found one specimen of Balanus bisulcatus, which had evidently been attached in an almost transverse position to a branch, and had thus become much distorted; so, again, I have seen specimens of the recent B. amaryllis attached irregularly to a Gorgonia, in the midst of the symmetrically elongated shells of Balanus navicula, an ally of B. calceolus.

This variety does not seem to attain so large a size as the ordinary form.

Affinities.—This species is allied to the two last-described fossils, namely, B. varians and unguiformis, but is perhaps more nearly related

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to the recent B. allium, an inhabitant of the Barrier Reef of Australia. The longitudinally folded variety (b) can hardly be distinguished by external aspect, or even by the opercular valves, from B. crenatus; but when the shell is disarticulated, the porose walls and non-porose basis of B. crenatus, allow of no mistake in the diagnosis of the two species.

2. Sub-Genus—ACASTA. Pl. 9.

ACASTA. Leach. Journal de Physique, tom. lxxxv, 1817.

Compartments six; parietes and basis non-porose: basis calcareous, cup-formed, not elongated, attached to sponges, or rarely to the bark of Isis.

Distribution mundane; imbedded in sponges and the sponge-like bark of Isis.

This sub-genus, in one sense, is a very natural one, inasmuch as all the species are closely allied in essential structure, in general appearance, and in habit. On the other hand, in the structure of the shell, in all the characters derived from the opercular valves and animal's body, Acasta cannot properly be distinguished generically from some species of Balanus; thus B. navicula and cymbiformis agree in the parietes and basis not being porose and in all other essential respects, differing only in the shell being more elongated in the rostro-carinal axis and in being attached to Gorgoniæ instead of to sponges; yet we shall see that Acasta purpurata lives imbedded in the bark of Isis, so that even the habit of being imbedded in sponges fails. Balanus terebratus would have been ranked as an Acasta had it inhabited sponges. On the other hand, some species of Balanus inhabit sponges, as is often the case with B. spongicola, and always with B. declivis; but both these species are distinguished easily from Acasta, the former by its porose walls and basis, and the latter by its membranous basis; it may, however, be reasonably doubted whether such differences ought to be considered as even sub-generic. The most important character of Acasta probably consists in the anterior ramus of the fourth pair of cirri, differing slightly

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in the arrangement of its spines, and in some other points, from the rami of the two posterior pairs of cirri,—a character not as yet observed in any other cirripede. Had not the genus Acasta been already founded and extensively admitted, certainly I should not have formed it; but considering the close similarity in habits, aspect, and structure, of the nine species of Acasta, and considering the already large size of the genus Balanus, I hope I may stand excused for admitting Acasta as a sub-genus.

General Appearance.—The shape varies from nearly globular to that of a somewhat flattened acorn, the orifice being often a little contracted from the inward curvature of the tips of the parietes. In A. spongites, however, the orifice is generally widely open; and, on the other hand, in A. sporillus, the orifice is reduced to a mere pore. The usual tint is pale reddish, but A. purpurata is purple, and A. sporillus purplish-brown. The surface is either smooth, or is shagreened with minute points, as in A. sporillus, and fenestrata, and in some specimens of A. sulcata; and in all the species, except A. sporillus and fenestrata, many individuals are furnished with elongated, curved, sharp, shelly points, like those in var. spinosus of Balanus tintinnabulum. The summits of the radii, which are generally of moderate breadth, are more or less oblique; their surface is often marked by lines parallel to the basis, instead of by vertical lines corresponding with the lines of growth, as in most species of Balanus. The carino-lateral compartments vary in proportional breadth in the different species: in A. sporillus, they tend to become rudimentary, and in this species (Pl. 9, fig. 9 b) their basal margins, or rather points, do not reach down to the basis. The species are all small, A. glans and undulata are the largest, being sometimes .55 of an inch in basal diameter.

Opercular Valves.—These differ in no generic respect from those of Balanus. The Scuta are striated longitudinally in several of the species: the adductor ridge is barely developed in any, being most prominent in A. cyathus. The articular ridge is prominent in A. fenestrata and purpurata. In the Terga, the spur is either truncated and very broad, or moderately narrow and bluntly pointed: the surface of the valve is often depressed, and in

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A. spongites and fenestrata it is furrowed in the line of the spur. The articular ridge and furrow are well developed in A. fenestrata and purpurata. The crests for the tergal depressor muscles are either absent or very feebly developed.

Structure of the Parietes and Radii.—The parietes are not porose; internally, they are either smooth, or slightly, or strongly ribbed in longitudinal lines; the presence of these ribs, which are homologous with the parietal septa in Balanus, is variable even in the same species. In A. sporillus the inner surface is curiously reticulated. The sutural edges of the radii are either smooth, or very slightly crenated by the septa, in lines parallel to the basis. The upper margins of both radii and alæ are always more or less oblique. The radii sometimes do not extend down to the basis; and in this case, as will presently be described, apertures are left in the lower half, between the compartments. In A. glans and lævigata the internal margin of the wall of each compartment, from the sheath to the basis, projects inwards, forming inside the shell as many double ridges (Pl. 9, fig. 5 b), as there are compartments, namely, six: a nearly analogous structure occurs in certain species of Balanus. The basal edge of the sheath, in most of the species (5 b, 9 b), depends freely, and is hollow beneath, but this is always a variable point.

Basis.—The base is either saucer or cup-shaped, but in A. cyathus it is almost flat; it is generally symmetrical and smooth, with the lines of growth closely approximate. In A. fenestrata the basis is commonly as deep, as the shell is high. The edge, in several of the species, is crenated with minute teeth or notches; and these are so large in some specimens of A. sulcata and cyathus, as to make the edge almost pectinated. In A. glans, and in a lesser degree in A. lævigata, there are six knob-like teeth (fig. 5 a), corresponding with the points of junction, between the basal edges of the inwardly prominent margins of the six compartments, and the basis: in those specimens, in which the six teeth are largely developed, six ridges produced by their successive development, extend down towards the centre of the basal cup. When the basal cup is dissolved in acid, there is left a little animalised tissue and an external membrane, formed as usual in slips, and furnished with blunt

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little external points (apparently representing spines), each of which has a short tubulus extending to the corium. Although I dissolved the basis of three specimens, I could not distinctly make out any cement; nor did I see any cement-ducts; yet these are readily distinguished, after the dissolution of the basis in acid, in Balanus, Elminius and Tetraclita. There can be no doubt that the young shell must at first be cemented to a fibre of the sponge; but I suspect that the cementing-tissue is not subsequently formed, owing to the support afforded by the growth of the enveloping sponge. As some species of Balanus are habitually or occasionally imbedded in sponges, it is important to observe, that the species of Acasta are not only imbedded, but are attached to the fibres of the sponge: but even this character, as we have already seen, is not sufficient to distinguish the genus Acasta from Balanus, for B. declivis is attached exclusively to sponge.

Perforations in the Shell.—Calcification seems often to fail to a certain extent in this genus: the basal cup in most specimens of A. spongites, and in some of A. glans and other species, is irregularly perforated by numerous minute orifices, closed only by the external membrane, and filled up inside by pulpy corium. In some specimens of A. spongites, from the Cape of Good Hope, parts of the basis were riddled like a sieve. I have seen similar perforations in the parietes of a few specimens of A. glans. In some specimens of A. sulcata, the radii do not extend quite down to the basal edge of the walls (Pl. 9, fig. 2 a), and in consequence a small cleft, closed only by membrane, is left between the compartments, for a little space above the basal cup. In A. fenestrata (fig. 7 a), and in a lesser degree in A. purpurata (8 a), not only do the radii not extend to the basal cup, but the parietes either on one or both sides of each suture are hollowed out, so that six, large or small, elongated, membrane-covered openings are formed, which extend from beneath the sheath down to the basal cup. These openings, which I have not seen in any other genus, will be more fully described under the respective species.

Mouth.—The parts of the mouth are identical in the several species, and present no generic differences from

20                          

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those in Balanus. The outer maxillæ and palpi appear unusually prominent: the labrum is deeply notched, with no teeth, or very obscure teeth on each side. The mandibles have five teeth, but the fifth is sometimes confluent with the inferior angle. The maxillæ are not notched; and carry one or two spines, near their inferior angle, nearly as large as the upper pair. The outer maxillæ are bilobed.

Cirri: in the first pair, the rami are very unequal in length, the one ramus being from half to one-third of the length of the other. The segments in the second and third pairs, are not so much broader, or so much more crowded with bristles, in comparison with the three posterior pairs, as is the case with most species of Balanus. The three posterior pairs, except in A. purpurata, are much elongated, and the long thin segments bear four, and sometimes only three, pairs of spines, which are generally doubly and finely serrated, or even feathered. The most remarkable fact respecting the cirri, is, that in A. spongites, sulcata, cyathus, and glans, the fourth pair, instead of being identical in structure, as in all other genera, with the fifth and sixth pairs, has, on its anterior ramus, the pairs of spines more crowded together, with the little intermediate spines, and those in the dorsal tufts, a little longer than in the sixth cirrus; and between the pairs of spines, there occur some straight, upwardly pointed, very minute, and very thick spines or teeth. And, what is still more remarkable (as will hereafter be described in detail), in certain specimens, but not in all, of A. sulcata, the front surfaces of the lower segments on the anterior ramus, are developed into thick, small, downwardly curved, hook-like teeth; this likewise is the case with the upper segment of the pedicel (Pl. 29, fig. 2).—a most elegant, mandible-like organ for the prehension of prey being thus formed. The variability of such beautifully contrived teeth is very surprising. Some similar teeth occur on the segments of the anterior ramus of the fourth cirrus, but not on the pedicel, in A. cyathus. A few teeth resembling the above, but thicker, occur on the segments of the anterior ramus of the same cirrus, in A. purpurata.

Branchiæ, &c.—In A. spongites, I found the branchiæ rather small, with transverse plications. The muscles of the

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sack, which run to the opercular valves, seemed rather feeble in most of the species. The penis in several species was remarkably long, and in A. spongites I noticed the straight projecting point at its dorsal base, as is common in Balanus.

Affinities, &c.—At the commencement of the description of the genus, I gave my reasons for keeping Acasta distinct as a sub-genus from Balanus. The species are particularly troublesome to identify, not only from the great variability of the most obvious characters, but from the very close general external appearance of most of the species, and the consequent necessity for cleaning and disarticulating at least one specimen in every group. The shape, however, of the shell and basis, and the state of their disarticulated edges, whether smooth, crenated, or toothed, here offer more serviceable, though still very variable, characters for the identification of the species, than is usual with sessile cirripedes; and this, probably, is in part due to the almost free or unattached condition of the whole shell, suspended, as it were, in the midst of sponges, which they inhabit. The opercular valves, on the other hand, are less serviceable than usual.

Range, Habitats, &c.—The species are found all over the world, excepting in the very cold latitudes.* Acasta lævigata ranges from the Red Sea to the Philippines; A. spongites from the south of England and Wales to the Cape of Good Hope; and A. cyathus from Madeira to the West Indies; most of the other species seem to have rather confined ranges. The East Indian Archipelago seems to be the metropolis of the genus, for here A. lævigata, fenestrata, purpurata, and sporillus, are all found. Of these four species, A. purpurata lives imbedded, not in sponges, but in the sponge-like bark of an Isis; and I think it probable, that A. sporillus may have somewhat analogous habits. The same species often lives imbedded in different kinds of sponge; thus, I have seen A. lævigata and cyathus in apparently three kinds, and A. spongites in, as I believe, four kinds. The genus existed during the miocene period, in the Coralline Crag, under a form closely allied to A. spongites.

* I am greatly indebted to Mr. Bowerbank for his great kindness, in looking over his immense collection of sponges from all parts of the world, and sending to me all the specimens of Acasta he could find imbedded in them.

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1. ACASTA SPONGITES. Pl. 9, fig. 1 a-1 d.

LEPAS SPONGITES. Poli. Testacea utriusque Siciliæ, 1795, Tab. 6, fig. 3-6.

BALANUS SPONGEOSUS. Montagu. Test. Brit. Suppl., 1808.

— SPONGITES. De Blainville. Dict. Sc. Nat., Pl. 116, fig. 3.

LEPAS SPONGIOSA. Wood's General Conchology, p. 47.

ACASTA MONTAGUI. Leach, in Lamarck, Animaux sans Vertèbres, 1818, et in Encyclop. Brit., Supplement, 1824, vol. 3, Pl. 57.*

— — J. E. Gray. Annals of Philosophy, New Series, vol. 10, Aug. 1825.

— SPONGITES. Philippi. Enum. Mollus. Siciliæ, vol. 2, p. 211, 1844.

BALANUS MONTAGUI. Brown's Illustrations of Conchology (2d edit. 1844), Pl. 53, fig. 24-26.

Carino-lateral parietes about one sixth of width of lateral parietes: inner surface of the parietes generally ribbed feebly: scutum with the articular ridge abruptly cut off at its lower end: tergum with the spur rounded-truncated, about one third of width of valve.

Hab.—South coast of England; South Wales, (Tenby); Portugal; Naples; Sicily; Cape of Good Hope.

This species and the three following, have caused me much doubt and trouble. At first I took the view here adopted, namely, that they were distinct: more careful examination made me run them altogether under one name. Finally, after still further deliberation, and the examination of a few additional specimens, I concluded there was the least chance of error in classing them separately. I may here mention, that in some sponge from the Cape of Good Hope, this species was mingled with Balanus spongicola.

* As the plate to the Supplement to the 'Encyclop. Brit.' is marked as engraved in 1817, I presume Dr. Leach gave a proof to Lamarck, thus enabling him to publish this species four years before the Supplement itself appeared.

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General Appearance.—The shape is usually that of a cup, the orifice being, in most cases, rather large, and deeply notched, owing to the great obliquity of the radii and alæ. The surface is generally smooth, but furnished with sharp calcareous projections. The colour is pinkish, and chiefly in the upper part of the shell; the lower part is often yellowish from the preserved epidermis. The parietes in the carino-lateral compartments are always narrow, being only one sixth or one seventh of the width of the parietes in the lateral compartments. The radii are not very wide, never equalling in width the parietes. The basis is moderately deep, and sometimes very deep, being even occasionally curled like a horn on one side. The specimens from Lisbon and Naples are a little larger than any British specimen which I have seen; the former being .3 of an inch in basal diameter.

Scuta: these are striated longitudinally in close lines, generally plainly, but to a variable degree. The whole valve is flat, thin, and rather elongated, with barely a trace of an adductor ridge: the articular ridge is short and rather prominent: it terminates downwards abruptly, and this does not appear to be the case in the two following species. Terga: these are small compared with the scuta, they are slightly beaked: the spur is truncated but rounded, more especially on the carinal side; it is rather more than one third of the width of the whole valve. The articular ridge and crests for the depressores muscles are feebly developed.

Structure of the Parietes and Radii.—The state of the inner surface of the parietes varies much; generally they are slightly ribbed close to the basis, the ribs sometimes extending up to the sheath; rarely the surface is quite smooth. The edges of the radii are slightly crenated. The upper internal surfaces of the radii, where overlying the alæ, are usually marked by feeble undulating lines, nearly parallel to the basis. The alæ have very oblique summits.

Basis: this is generally of a regular cup-like form, and about two thirds as deep as the shell is high; sometimes it is pointed at the bottom and distorted. The edge is feebly crenated, and rarely quite smooth. It is often penetrated by small rounded irregular holes; and I have seen specimens from the Cape of Good Hope with parts like a sieve.

Cirri: in the first pair, the anterior ramus is nearly thrice as long as the posterior ramus. The second cirrus is short, with one ramus longer by three or four segments than the other ramus; the terminal segments are truncated. The third cirrus is about one third longer than the second cirrus. In the anterior ramus of the fourth pair, the regular pairs of spines are rather crowded together in the upper part of each segment, and the intermediate little spines and dorsal tufts are rather long in comparison with those of the fifth and sixth pairs of cirri: moreover, amongst the regular pairs, a few very minute and thick spines, pointing upwards, could be perceived. So that we here have the very unusual case of the fourth cirrus not exactly resembling the fifth and sixth pairs; and we shall see, in the following species, that this same anterior ramus of the fourth cirrus presents in addition another very extraordinary character. In the sixth cirrus there are on each segment four pairs of spines.

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2. ACASTA SULCATA. Pl. 9, fig. 2 a-2 d.

ACASTA SULCATA. Lamarck. Animaux sans Vertèbres, 1818.

— — Deshayes, in Guerin, Magasin de Zoologie, 1831, Tab. 24.

Carino-lateral parietes about one sixth of width of lateral parietes: inner surface of the parietes generally ribbed strongly: basis with the edge strongly crenated: orifice of shell rather small: tergum with the spur generally truncated and nearly half as wide as valve.

Var. (a) fig. 2 b: with the walls externally ribbed.

Var. (b) fig. 2 a: with small membrane-covered clefts between the edges of the walls, close above the basal cup.

Hab.—Sidney, Port Fairy, Moreton Bay in lat. 27° S., New South Wales; Southern Australia; and, according to Lamarck, Western Australia, in lat. 25° S. Mus. Brit., Cuming, Bowerbank, &c.

I am almost ashamed to admit this species, so small are its differences compared with A. spongites; yet I think that it probably is a distinct form.

In general appearance and character this species comes very near to A. spongites. As in the latter, the parietes of the carino-lateral compartments are narrow.* The orifice seems always to be smaller. Internally, the parietes are generally much more strongly ribbed, and the edges of the basal cup more plainly crenated. The sheath is generally coloured of a brighter pink, sometimes tinged with orange. The average largest specimens (from .3 to .5 of an inch in basal diameter) are a little larger than the largest European specimens: I have seen one specimen from Moreton Bay .4 in basal diameter, and from the basal cup being very deep, actually .75 in height. The scutum has the articular ridge not so prominent and not so abruptly cut off at the lower end, as in A. spongites: on the other hand, the adductor ridge seems rather more prominent; but these differences are trifling. In the tergum the breadth of the spur (fig. 2 c, 2 d) varies in specimens taken out of the same branch of sponge; some can hardly be distinguished from the

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* In Mr. Cuming's collection there is a specimen, from Sidney, which I fully believe to be the present species, but cannot be positively sure, as the opercular valves have been lost, which is very remarkable from the walls of the carino-lateral compartments being reduced to the thickness of a mere thread, not one twentieth of the width of the lateral compartments; we here see the structure of Acasta sporillus prefigured.

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same valves in A. spongites, but generally the spur is broader and squarer.

This species presents some remarkable varieties: in one specimen, from Sydney, the parietes were externally ribbed longitudinally (fig. 2 b), the ribs being roughened with minute points, giving to the shell an elegant appearance; and this without doubt is the A. sulcata of Lamarck, procured by Peron at Shark's Bay, lat. 25° S., on the opposite of the Australian continent: some specimens from Port Lincoln, in South Australia, were not ribbed, only smoothly striated in longitudinal lines: although both sets of specimens had almost smooth scuta, and were thus different from common specimens, yet there could be no doubt, from their similarity in all other points, that they did not differ specifically from them, though the latter had their scuta striated, but not their parietes. Hence we see that there is no relation between the striæ on the parietes and on the scuta. The Port Lincoln specimens, and some others, were remarkable from the radii not extending down to the basal cup, a minute cleft, covered only by membrane, being thus left along the sutures, low down between the parietes (fig. 2 a); we shall see this singular structure strongly developed in A. perforata. Owing apparently to these clefts, the edge of the basal cup, exhibited traces of six knob-like teeth, like those characteristic of A. glans.

Cirri.—The cirri resemble those of A. spongites, with the exception that the segments on the posterior pairs bear only three main pairs of spines. With respect to the anterior ramus of the fourth pair of cirri, the following very singular facts were observed:—in a specimen from New South Wales (var. with the tergum having a narrow spur), on two or three of the lower, but not on the lowest, segments, the front margin was produced or developed into two or three minute, thick teeth, slightly curved like hooks downwards: in other specimens from New South Wales (var. with the tergum having a broad spur, and inhabiting the same branch of sponge with the last-mentioned variety), there was no trace of these teeth. But again, in two other specimens with the tergum having a broad spur (collected by different persons, near Sydney), and in another from South Australia, this structure was carried to an extreme, for in these (as represented, Pl. 29, fig. 2) there were beautifully formed teeth on the fourteen lower segments (the twelve upper being without them), and likewise on the upper segment of the pedicel. These teeth are graduated in size on each segment; they are admirably adapted for securing any prey; and, in fact, they convert each segment into a mandible-like organ. On the segments, on which these teeth are well developed, some of the regular pairs of spines are aborted.

Diagnosis.—Finally, this species, if it be, as I believe, distinct, differs from A. spongites only in the internal surface of the parietes being more strongly ribbed and brighter coloured,—in the edge of the basal cup being more plainly crenated,—in the articular ridge of the scutum being of a different shape,—in the spur of the tergum being often broader,—in the segments of the posterior cirri having only three pairs of main spines,—and, lastly, in the occasional presence of the hook-like teeth on the anterior ramus of the fourth cirrus.

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3. ACASTA CYATHUS. Pl. 9, fig. 3 a-3 c.

Carino-lateral parietes about one fourth of width of lateral parietes: radii wider than the parietes: basis nearly flat, small: tergum with the spur truncated, half as wide as valve.

Hab.—Madeira, Mus. Lowe, and Bowerbank, West Indies, Mus. Stutchbury. Hab. unknown, Mus. Brit.

I feel more confidence in this case, than in that of A. sulcata, that we here have a distinct species, though at one time I treated it only as a marked variety of A. spongites. I rely chiefly on the great proportional width of the radii of all the compartments, and on the width of the carino-lateral compartments, compared with the lateral compartments, and on the general shape of the shell, which differs considerably from that of the two previous forms: in consequence of Acasta being attached to and imbedded in a yielding substance, such as sponge, I believe external form to be of more value as a specific character in this genus, than in most sessile cirripedes. I have examined specimens taken out of the yielding Spongia officinalis and out of an unusually compact sponge, and they resembled each other in every respect.

General Appearance.—Colour pale pink, or that of flesh: basis remarkably flat and rather small, with the walls above bulging out a little. The radii are very wide, being wider than the parietes to which they belong: the orifice is generally rather large. The parietes of the carino-lateral compartments vary from one third to one fourth of the width of the parietes of the lateral compartments. Basal diameter of largest specimen .35 of an inch. Internally, the parietes are generally more strongly ribbed than in A. spongites.

The Opercular Valves are large, owing to the form of the shell. The Scuta present no particular character, and are not distinguishable from those of A. sulcata; but the adductor ridge is perhaps rather more developed. The Terga (Pl. 9. fig. 3 c) are nearly as large as the scuta, and this is an unusual circumstance; the spur is more than half as wide as the valve; it is placed not quite close to the basi-scutal angle; on the carinal side, the basal margin of the valve slopes a little towards the spur. I may mention, that in several specimens from Madeira, the scuta and terga, on one side, had grown to a monstrous thickness.

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Cirri: these resemble, in every respect, those of A. spongites, with the remarkable exception that on the anterior ramus of the fourth cirrus, several segments were furnished with the beautiful downward curved, mandible-like teeth, as in A. sulcata; but differently from in that species, there were none on the upper segment of the pedicel. I should have thought this an excellent specific character, had not these teeth been so extremely variable in A. sulcata.

Finally, I think this species is more nearly related to A. sulcata than to A. spongites.

4. ACASTA UNDULATA. Pl. 9, fig. 4.

Shell, apparently, as in A. spongites, but larger: scutum marked by longitudinal ridges, often in pairs, with the intermediate furrows rather wide: spur of tergum nearly half as wide as valve.

Fossil in Coralline Crag (Sutton), Mus. S. Wood.

I owe to Mr. Wood the inspection of a fine suite of separate valves. Owing to the shell never having been found entire, its general shape is not known, and, what is of more consequence, the relative proportional width of the parietes of the carino-lateral compartment is unknown. I have (but with doubt) given it a distinct specific name, owing to the peculiar character of the furrows on the scuta, and to the large size of the whole shell. In its other characters it comes nearest to A. spongites, excepting in the spur of the tergum, which resembles that of A. sulcata.

The compartments appear to have been rather smooth externally. The radii are not wide, as in A. cyathus; and the basis is cup-formed. Internally, the parietes are feebly ribbed, as in A. spongites. Judging from the dimensions of the separated valves, this species must have equalled and perhaps exceeded the size of the largest living species, namely, A. glans, from Australia. Hence we may infer, that the basal diameter probably exceeded .55 of an inch: I may add, that the largest European specimens of A. spongites, from Naples and Portugal, are only .3 of an inch in basal diameter.

Scuta.—These seem to resemble the scuta of A. spongites in all respects, except in the longitudinal ridges standing much further apart, and, consequently, in the furrows being much wider: each ridge is generally double. Although there is a good deal of variability in the character of these ridges in A. undulata, and likewise in A. spongites,

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I have not seen any form intermediate between them. It must, however, be confessed, that this is an extremely variable character in many sessile cirripedes. In the Terga, the spur is about half the width of the whole valve, and therefore rather wider than in A. spongites.

5. ACASTA GLANS. Pl. 9, fig. 5 a-5 c.

ACASTA GLANS. Lamarck. Animaux sans Vertèbres, 1818.

Parietes internally quite smooth, with the lateral margins of each compartment inwardly prominent: basis with the edge rarely crenated, but furnished with six inwardly prominent teeth: scutum strongly striated longitudinally.

Var. (a) with the edge of the basal cup finely crenated.

Hab.—New South Wales, Southern Australia; Mus. Brit., Stutchbury, &c.

This fine species seems to be extremely common, imbedded in an open porose sponge on the eastern and southern shores of Australia. It is very distinct from the other species, with the exception of the following A. lævigata, which, with some hesitation, I have allowed to remain specifically separated.

General Appearance.—Excepting in its larger size, this species differs in external appearance but little from A. spongites; its colour is pale dirty reddish. The surface is generally studded with small calcareous points. The parietes of the carino-lateral compartments are about one fourth of the width of the parietes of the lateral compartments, and therefore proportionally of the same width as in A. cyathus. The largest specimen which I have seen, was .55 of an inch in basal diameter.

Scuta.—These are slightly narrower, thicker, and more convex than in A. spongites: they are strongly striated in longitudinal lines. The articular ridge is very feebly developed. Terga: in full-grown specimens, the spur is half the width of the whole valve, and is truncated; its basal edge being parallel to the basal margin of the valve. The articular ridge and crests for the depressores muscles are very feebly developed.

Internal structure of the parietes.—The inner surface of the parietes is quite smooth, without even a trace of ribs or teeth. But the most important character is that the internal lateral margins on both sides of each compartment, from the sheath to the basis, project inwards and form a rim; so that when the shell is viewed from within (Pl. 9,

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fig. 5 b, representing the lateral and carino-lateral compartments, and part of the carina), the six sutures are seen to be strengthened by six double columns.

Basis.—This is moderately cup-formed. The edge, in order to meet the basal points of the inwardly projecting lateral margins of the six compartments, has six knob-like teeth. These are placed at unequal distances, for two on each side stand near each other, owing to the narrowness of the carino-lateral compartments. The degree of their development varies extremely; when most developed, as in the specimen figured (Pl. 9, fig. 5 a), each tooth is bifid and a little hollowed out, so as to receive the points of the two inwardly projecting margins which form each suture. Ridges, more or less prominent, running from each of the six marginal teeth, extend towards the centre of the cup. These six teeth cannot be seen from the outside. The edge of the cup is rarely crenated; but I have seen two instances in which this was the case.

Cirri.—In the first pair, the rami are not quite so unequal as in A. spongites; the longer ramus being about twice as long as the shorter. In the third pair, there are some very minute, thick, upwardly-pointing spines, which I did not notice in A. spongites. In the fourth pair, the spines are a little more crowded, with longer dorsal tufts, than in the sixth pair; and they are mingled with some very minute, thick, upwardly pointing spines. In young individuals, there are only three pairs of main spines on the segments of the sixth pair, instead of four pairs.

6. ACASTA LÆVIGATA. Pl. 9, fig. 6 a, 6 b.

ACASTA LÆVIGATA. J. E. Gray (!) Annals of Philosophy, (new series), vol. 10, Aug. 1825.

Parietes internally quite smooth, with the lateral margins of each compartment inwardly prominent: basis with the edge strongly crenated, and furnished with six inwardly prominent teeth: scutum feebly striated longitudinally, or smooth.

Var. (a), epidermis coloured dull orange.—Red Sea.

Hab.—Red Sea, Philippine Archipelago; Mus. Brit., Cuming, &c.

This species, of which I have examined many specimens from the above two and other unknown localities, agrees in all essential points of structure with A. glans, and consequently I for some time classed them together; but the characters, though usually of small value, by which this form differs from A. glans being apparently constant, I

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have with some doubt allowed it to remain specifically distinct. These characters are, firstly, the much smaller size of the whole shell in A. lævigata; secondly, the edge of its basal cup being always crenated, which seems to be a rare accident in A. glans; thirdly, though of secondary importance, the scutum being here less plainly striated; and, lastly, the spur of the tergum being of less breadth, and of a more rounded outline; on the other hand, it must be confessed, that when small specimens of A. glans are taken, there is hardly any difference in the spurs of the terga.

General Appearance and Structure of Shell.—The surface of the shell is often very smooth, but is sometimes studded with some small sharp calcareous points. The colour is white, or pale reddish-brown; but in the specimens from the Red Sea, the tint is more orange, with the upper part of the shell white. The orifice of the shell is unusually small. The largest specimen which I have seen was only .25 of an inch in basal diameter, and therefore less than half the size of A. glans. The internal surfaces of the parietes are smooth, with the two lateral margins inflected, as in A. glans. The edge of the basal cup has six knob-like teeth, like those in A. glans, but smaller; and, in addition, it is finely crenated.

Scuta: these differ only in being less plainly striated in longitudinal lines; indeed, some specimens show hardly a trace of this structure. Terga; these valves, in some varieties (Pl. 9, fig. 6 b) can hardly be distinguished from those of equal size from young individuals of A. glans; other varieties have the spur (Pl. 9, fig. 6 a) not truncated, but broadly pointed, and therefore of considerably different shape.

Neither in the mouth, nor cirri could I detect any difference with A. glans.

7. ACASTA FENESTRATA. Pl. 9, fig. 7 a-7 c.

Shell reddish, with six large, membrane-covered apertures between the sutures, above the basal cup: carino-lateral parietes half as broad as lateral parietes; internally, parietes and edge of basis smooth: tergum with the articular ridge short and prominent; spur pointed.

Hab.—Philippine Archipelago, Mus. Cuming.

General Appearance.—Shell rather elongated or tubular; with the upper part reddish, and the surface roughened with very minute points. The basal cup is generally as deep as the shell is high, ending down-

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wards in a blunt point, often curved to one side. The summits of the radii, as usual, are oblique. The parietes of the carino-lateral compartments are about half as wide as the parietes of the lateral compartments, and are therefore of greater proportional width than in the foregoing or any other species of the genus. The large membrane-covered openings, or, as they may be called, windows, presently to be described, between the lower halves of the compartments, is much the most remarkable character of this species. The largest specimen which I have seen was only .23 in diameter, and .6 of an inch in height, measured from the basal point of the cup to the tips of the compartments.

Scuta:These barely exhibit a trace of longitudinal striæ. The valve is rather thick and convex. The basi-tergal angle is much rounded off. Internally, the articular ridge is thick and rather prominent. Terga: the valve is furrowed in the line of the spur: the spur is pointed and rather long; it is distinctly separated from the basi-scutal angle of the valve, and the basal margin on the two sides of the spur forms a straight line. The articular ridge is prominent, and short.

Structure of the Parietes, Radii, and Basis.—The parietes are internally quite smooth down to its basis. The edges of the radii are also smooth, as is the edge of the basal cup. The alæ project less than usual. The radii are of moderate breadth, they extend downwards only a little below the sheath, namely, about half way down the shell, where they terminate, as usual, in a point. The increase in width, during growth, of the radii, and their not extending down to the basis, would necessarily cause a gap between the opposed edges of the walls, in the portion beneath the radii; but besides this, the edges of the walls themselves, beneath the radii, and on the opposed side beneath the alæ, are hollowed out, but on the latter side or beneath the alæ sometimes in a lesser degree. The result of this is, that the compartments, in their lower halves, are separated from each other by membrane-covered windows or apertures, arched at their upper ends, and of considerable size, namely, about as wide as the parietes of the carino-lateral compartments. I have only further to remark, that during the downward growth of the parietes, the apertures increase in size, but at the same time become closed up at their upper ends; and the arched layers of shell added at these upper ends, assume a very different aspect from the rest of the parietal surface,—appearing like two wedges, with their points upwards, let in, on one side of the suture, between the ordinary parietal surface and the radius, and, on the other side of the suture, between the ordinary parietal surface and the recipient furrow of the radius.

The animal's body was in a bad state of preservation; but, as far as I could make out, the cirri resembled those of A. glans.

Affinities.—This species differs from A. glans in not having the internal margins of the compartments projecting inwards. It differs from all the ordinary varieties of A. spongites, in the smoothness of the basal edges of the parietes and of the edge of the cup; in the greater width of the carino-lateral compartment, though this is a variable point in A. spongites; slightly in the shape of the scuta and terga; and, lastly, in the large, membrane-covered openings between the compartments.

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8. ACASTA PURPURATA. Pl. 9, fig. 8 a-8 c.

Shell dull blueish-purple, with six small, membrane-covered apertures between the sutures, close above the basis: tergum with the articular ridge very short and prominent; spur very broad and rounded.

Hab.—Sumatra; Philippine Archipelago; imbedded in the bark of an Isis; Mus. Cuming, Stutchbury, Brit.

This species is perfectly distinct from the others, as shown by its general appearance, its habits, and the structure of its opercular valves: it is allied to A. fenestrata, in having membrane-covered apertures between the compartments, and in some respects in its opercular valves: it is also allied to A. sulcata and cyathus in the parietes being often internally ribbed, in the basal cup having a crenated edge, and in the anterior ramus of the fourth cirrus being furnished with the minute hook-like spines.

General Appearance.—Sub-globular, slightly compressed, with a rather small orifice; smooth, but sometimes furnished with sharp shelly points; dull purple, more or less dark, with the upper parts of the walls often white. The radii are rather narrow, and generally white, with their summits only slightly oblique, but variable in this latter respect. The parietes of the carino-lateral compartments are narrow, being only one sixth of the width of the parietes of the lateral compartments. In some specimens there are membrane-covered apertures of considerable size, in others mere narrow clefts, between the basal halves of the compartments. The basal cup is moderately deep. The largest specimen was only .16 of an inch in basal diameter.

Scuta, rather broad, externally convex, not longitudinally striated: articular ridge prominent, short, not extending down above one third of the length of the valve. Depression for the adductor muscle deep. On the internal surface, near to the rostral angle, a rather large purple spot of corium adhered to the valve. Terga, broad, externally rather convex: scutal margin protuberant: carina margin slightly inflected, or furnished internally with a rim: articular ridge prominent, very short, not extending down above one fourth of the valve. Spur very broad, rounded, confluent with the basi-scutal angle of the valve.

Internal Structure of the Parietes, Radii, and Basis.—The parietes, internally, are either quite smooth, or more commonly ribbed, with the

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basal edge in consequence crenated; the ribs are either placed at an unusual distance from each other, and consequently are few in number, or are pretty close together. The edge of the basal cup is either quite smooth, or closely crenated, or distantly toothed, in conformity with the state of the internal surface of the parietes. The radii have nearly smooth edges, with their summits more or less oblique. They sometimes extend down only three fourths, or only two thirds, of the length of the shell, and the margins of the parietes under the radii being a little hollowed out, the sutures are converted into clefts or apertures (of course covered by membrane) like, but not so large as, those in A. fenestrata. The margins of the parietes are hollowed out only on the side of the radius, and not on both sides of the sutures, as is most usual in A. fenestrata. In some specimens the radii extended down close to the basal cup, and only very minute clefts were left between the opposed edges of the parietes.

In the animal's body the only noticeable character was, that on the anterior ramus of the fourth pair of cirri, some of the segments were furnished with very broad and thick, small, downwardly curved, teeth or hooks, like those described in certain varieties of A. sulcata; but they are here stronger and thicker. The segments in the three posterior pairs of cirri are not so much elongated, as in the other species.

9. ACASTA SPORILLUS. Pl. 9, fig. 9 a-9 d.

Shell purplish-brown, with the parietes internally strongly ribbed and reticulated: carino-lateral compartments extremely narrow, not extending down to the basis.

Hab.—Sooloo Islands, East Indian Archipelago; Mus. Dana.

I am indebted to Mr. Dana, the distinguished naturalist of the United States Antarctic Expedition, for two specimens of this interesting species, which, in the singular reticulated structure of the inner surface of the walls, and in the almost rudimentary condition of the carino-lateral compartments, not extending down to the basal cup, is very distinct from the foregoing species. I have used Mr. Dana's very appropriate MS. name of sporillus. The specimens were dredged up, lying quite loose and unattached at the bottom of the Sooloo sea; the one which I opened, must have long lain dead; but Mr. Dana assures me that some were living, and he has sent me drawings of parts of the mouth and cirri: I am much surprised at this circumstance;

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for analogy would have made me believe that this species must have been imbedded in some sponge-like body, such as the bark of a zoophyte, and that it could not have lived unattached. I may add that a small fragment of a brown leathery substance adhered to the upper end of one of the two specimens, and this seems to indicate attachment.

General Appearance.—Shell shaped like a pointed acorn; slightly flattened; orifice extremely small; surface very finely punctured, covered by a purplish-brown epidermis, with transverse stripes of different shades, and with the apex dark; according to Mr. Dana, when fresh, the colour was purplish-carmine. Radii narrow, white. The carino-lateral compartments are extremely narrow; the wall-portion (fig. 9 b) forming a mere linear rib, terminating downwards in a sharp point, which does not reach the basal cup: hence this compartment evidently tends to become rudimentary. The basal cup is moderately deep and pointed. Basal diameter .16; height, from the bottom of the cup to the top of the shell, .24 of an inch.

Scuta: narrow, with the upper part produced; not striated longitudinally; coloured by a pale purple, longitudinal band. Internally, there is scarcely a trace of an articular ridge, which, in the other species, is always more or less developed. Terga with the spur bluntly pointed; nearly the whole basal margin, on the carinal side, slopes towards the spur.

Internal Structure of the Parietes, Radii, and Basal Cup.—The parietes are strongly ribbed internally; and these ribs are connected by very narrow, less prominent, transverse, slightly branched ridges, giving a reticulated structure to the inner surface. Between several of the main longitudinal ribs, in the lower part of the shell, new ribs may be seen in process of formation, and these tend to convert the reticulated structure into a double row of minute cells. I have not met with an exactly similar structure in any other cirripede; but I have no doubt that the little transverse ridges are homologous with the transverse calcareous septa in the parietal pores of many Balani, in the same manner as the internal longitudinal ribs, in this and other species of Acasta, are homologous with the longitudinal septa forming the above pores. The edge of the basal cup is pectinated with teeth, which lock into the teeth formed by the ends of the internal parietal ribs. The radii are narrow, and have smooth edges. The alæ project beyond the parietes to a remarkably small extent. The sheath is free, or hollow beneath. I have already described the almost rudimentary condition of the carino-lateral compartments; this is best exhibited in an internal view of the two compartments, as given in Pl. 9, fig. 9 b.

Animal's body unknown to me: from Mr. Dana's drawing the three posterior pairs of cirri seem to have been much elongated: and the rami of the first pair, as usual, unequal in length.

M. Deshayes has given an indifferent figure and imperfect description of ACASTA TUBULOSA (Guerin, Magasin de

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Zoologie, 1831, Tab. 39; and Guerin, Iconographie du Règne Animal, Mollusques, Tab. 38, fig. 4, but here by a misprint called A. spinulosa); it is utterly impossible to recognise the species of this genus from such materials.

3. Genus—TETRACLITA. Pl. 10, 11.

TETRACLITA. Schumacher. Essai d'un Nouveau Syst., &c., 1817.

CONIA. Leach. Journal de Physique, tom. 85, 1817.*

ASEMUS. Ranzani. Memoire di Storia Naturale, 1820.†

POLYTREMA. De Ferussac. Dict. Classique d'Histoire Naturelle, 1822.

LEPAS. Gmelin. Systema Naturæ, 1789

BALANUS. Bruguière. Encyclop. Method., 1789.

Lamarck. Animaux sans Vertèbres, 1818.

Compartments four, sometimes externally calcified together: parietes permeated by pores, generally forming several rows. Basis flat, irregular, calcareous, or membranous.

Hab.—Throughout the tropical and warmer temperate seas.

General Appearance.—The shell is conical, more or less depressed, and very rarely, even when growing in crowded groups, becomes cylindrical or elongated. The orifice is seldom large, generally diamond-shaped or oval. The colour is either nearly white or purple, occasionally even inky black, or very dark green, and sometimes of a pale pink peach-blossom. The surface is sometimes smooth, but more commonly longitudinally ribbed; the outer lamina of shell is very often wholly corroded away, excepting close to the basis, leaving the solidly upfilled parietal tubes exposed: these give the shell a striated appearance, or they appear like flattened tapering points adpressed to its surface (Pl. 10,

* From a note by the Editor, it appears that Schumacher's essay appeared before the number of the Journal containing Leach's paper, so that Schumacher's name must be adopted.

† I have not seen a complete copy of this work, and give the title from a catalogue; the running heading of the part containing the Cirripedia, is "Opuscoli Scientifici."

21                       

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fig. 1 b): Lamarck attempted to express this appearance, by using the specific name of stalactiferus. The colour of the shell depends, to a considerable extent, on the colour of the shelly matter in these exposed parietal tubes. We shall presently see that the corrosion and disintegration, to which some of the species are so liable, plays an important part during their growth. The radii are either well developed, as in most of the species; or they are entirely absent, as in the great majority of specimens of T. porosa and serrata. In many individuals of T. porosa and purpurascens not only are the radii absent, but the four compartments are calcified together without any trace, on the external surface, of the sutures. The largest specimen which I have seen of T. porosa, which is the largest species, was two inches in basal diameter, and nearly one inch and a half in height.

Scuta.—These valves are sub-triangular, and either longitudinally or transversely elongated. Externally, the growth-ridges are moderately prominent, and in T. costata and cœrulescens they are crossed by longitudinal striæ. Along the occludent margin, the inflected extremity of each alternate growth-ridge is generally much thickened,—a set of teeth being thus formed, by which the two valves are locked together. In T. porosa, this character is variable, for sometimes every alternate ridge, and sometimes only two or three ridges, separated from each other by several growth-ridges, are thus developed into teeth. The articular ridge is either moderately prominent, or is extremely prominent, as in T. cœrulescens; but the lower edge in no case depends as a free, hinge-like style, as sometimes in Balanus. The adductor ridge is generally well developed and distinct from the articular ridge: in T. purpurascens it is very blunt: in T. serrata it is united to the articular ridge half way up it, thus forming a deep tubular cavity running up to the apex of the valve: in T. cœrulescens, the adductor ridge is very short, and is united to, or almost continuous with, the lower end of the articular ridge, a small sub-cylindrical tubular cavity being thus formed. Small crests exist for the attachment of the rostral and lateral depressor muscles, in most of the species, excepting T. purpurascens and costata, in which, however, more especially in the former, there are,

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instead of crests, minute pits for the attachment. These crests vary much in prominence in the same species.

Terga.—These valves present no essential differences from those of Balanus; they are sometimes beaked, and the beak is hollow and occupied by a thread of corium, as in that genus. The external surface of the valve is often depressed in the line of the spur, but there is never a longitudinal furrow with the edges folded in, as in Balanus. The spur is very short in T. purpurascens. In T. radiata, the articular ridge is remarkably prominent. The crests for the depressor muscles are well developed in all the species. The shape of the terga is variable in nearly all the species, and greatly so in T. porosa.

Compartments.—Owing to there being only four compartments, the lateral pair are large; the size of the carina relatively to the rostrum varies, according as its alæ have been added to during diametric growth. The walls are very thick, and are composed of numerous tubes, in some species as many as fourteen or fifteen rows being exposed on the basal margin (Pl. 10, fig. 1 g). The tubes are generally angular, and slightly elongated in the ray of the circular shell; sometimes they are nearly circular and small. New tubes are formed only at the basal edge of the outer lamina, by the bifurcation of the septa which form the tubes. In very young specimens there is only a single row of tubes; and in T. rosea this holds good throughout life: in this species (fig. 3 d) the tubes, in the single row, are large and quadrangular, and the outer lamina of shell is strengthened by numerous, small, internal, longitudinal plates. I believe the branching septa, which separate and form the parietal tubes, correspond with the longitudinal septa in the more simple walls of Balanus. The tubes become solidly filled up, in their upper parts, with hard, and generally coloured shelly matter. The degree to which they are filled up differs in the different species; the external side of each tube is always first thus coated. The thin outer lamina of shell, in several of the species, commonly disintegrates and disappears; the upfilled parietal tubes being thus exposed. The inner lamina of the walls is generally smooth, but in T. radiata it is longitudinally ribbed, as in most species of Balanus. The sheath is generally dark-

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coloured; its lower edge does not project or overhang the inner lamina, as is usual in Balanus, excepting in T. serrata, and in some few varieties of T. porosa.

The Radii, when developed, are either narrow or broad, with their summits either oblique or extending in a straight line from the top of one compartment to that of another. In T. serrata, I have not seen a single specimen with the radii developed; in T. porosa, they are very seldom developed, and then, apparently, only in quite young specimens, in which they are narrow; in T. purpurascens, they seem to be about as often developed as not, and when present they are broad; in T. costata, cœrulescens, and radiata, they are always largely developed. In some specimens of the species, in which the radii are not developed, even the sutures do not reach the external surface; the outer lamina of the parietes being continuous all round, so that the shell seems formed of a single piece. Even in such specimens, the four compartments, viewed from within, can be seen to be distinct; and the sutures can generally be traced across the whole thickness of the parietal tubes; in this latter case, when the sutures are broken open, the radii are seen to be represented (Pl. 10, 1 h) by a few small sinuous ridges. Owing to the disintegration of the upper and outer part of the shell, and the consequent exposure of parts of the sheath and alæ, the radii sometimes appear as if developed, when such is not the case. With respect to the internal structure of the radii, they are formed, in T. purpurascens and costata, of tubes, like those of the parietes, and therefore according to the normal plan; whilst in the other species they are formed by longitudinal sinuous ridges, sending out on each side irregular denticuli; and the interspaces between the ridges are filled up solidly during the growth of the radii, in all the species, except in T. radiata, in which they are left to a considerable extent open. These sinuous ridges, with their denticuli, homologically represent the branching septa which form the parietal tubes. The edges of the alæ are crenated in all the species, except in T. costata.

Diametric growth.—When first examining groups of T. porosa, in none of which the radii had been developed, and in which, consequently, the shell could not have grown in

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diameter, but only at its basal margin, I was at first unable to comprehend, how the upper part of the shell and the orifice could have acquired their proper proportional width. The young shell, at its first formation, starts with an orifice so small that a pin could hardly be inserted in it; and this in many individuals is never increased in diameter by the diametric growth of the shell; but in place of this, as the conical shell is added to at its base, the whole upper part disintegrates and wears away, the orifice becoming thus enlarged. We thus see that the corrosion and wearing away of the upper part of the shell is a necessary element in its growth. The development of the radii, which in some of the species, as in T. purpurascens, at first seems to be quite capricious, really depends upon the fact, whether the specimens have been exposed to disintegration; for I have almost always found that when the outer lamina of shell has been well preserved, the radii have been developed, and the orifice has been enlarged by their growth, instead of by the wearing down of the upper part of the conical shell.

Basis.—This consists of a very thin, flat, though irregular, translucent, calcareous plate, which towards the edges is sometimes membranous. In T. purpurascens, the basis is entirely membranous. When a portion of the calcareous base is dissolved in acid, a tissue is left, composed of several laminæ, to which numerous bifurcating cement-ducts are attached: even before dissolution, these delicate bifurcating ducts can just be perceived by the aid of a simple lens.

Mouth.—The several organs present no particular characters. There are generally three teeth on each side of the notch in the labrum. The palpi usually have parallel sides, but are club-shaped in T. purpurascens and costata. The mandibles have generally four teeth, but there are five in T. vitiata, and only three in T. costata. The maxillæ are notched. The outer maxillæ are bilobed in front.

Cirri.—The segments of the three posterior pairs usually support only three pairs of main spines, but there are four pairs in T. vitiata and costata: between each pair, there is either a tuft of fine spines, or a single fine spine. The rami of the first cirrus are unequal in length. In the third cirrus, the posterior ramus is sometimes much elongated, but some-

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times both rami are short and blunt. Some of the segments in the third cirrus often support very coarsely and doubly pectinated spines. Under the head of T. porosa, it will be seen to what a remarkable degree the relative numbers of the segments in the several cirri vary, even in specimens taken out of the same cluster.

The Branchiæ are well developed (at least in T. porosa and costata), as a large, plicated, tapering fold, with a small second fold on the inner side at the base. In T. porosa the stomach is destitute of cæca. The vesiculæ seminales in this same species are large, with their broad, blunt ends reflexed. The ovarian tubes surround the sack, and cover the basal plate.

Distribution and Habitats.—This genus is confined to the tropics, and to the warmer parts of the temperate seas: in the southern hemisphere, it ranges south, to the Cape of Good Hope and to Van Diemen's Land: in the northern hemisphere it does not appear to range so far; I do not know of any authentic case of a species having been found in the Mediterranean, or on the shores of the United States, north of the West Indies. Tetraclita porosa is found round the whole world; T. radiata, also, has a very wide range, inhabiting the West Indies, the East Indian Archipelago, and New South Wales. This latter species, as well as T. cœrulescens, is often attached to the bottoms of ships, adhering to Balanus tintinnabulum. The several species live attached to tidal rocks, to littoral shells, or to massive corals. I have met with two instances, in the West Indies and the Philippine Archipelago, of T. porosa adhering to wood. Tetraclita porosa seems to feed chiefly on crustaceans: the number and the size of the amphipods, isopods, and entomostracans, together with an annelid, in the stomachs of some specimens from South America, was quite surprising. As many as five species occur in the same region, in the eastern half of the world; thus on the shores of New South Wales, we have T. porosa, vitiata, radiata, purpurascens, and rosea; in the Philippine Archipelago, we have T. porosa, vitiata, costata, and cœrulescens.

I have not seen any species of this genus fossil.

Variation.—The species vary in shape nearly, but not

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quite as much as in Balanus, for we very rarely here see cylindrical varieties; but in the same species, we have extremely depressed, steeply conical, and convex forms; the orifice varies in relative size; the state of the surface, whether ribbed or smooth, whether well preserved or corroded, the upfilled parietal tubes being thus exposed, varies more than in Balanus. The colour also varies; specimens of T. porosa (Pl. 10, fig. 1 a to 1 f ) being dark purple, or even inky black, white, pale pinkish-purple, and green: as far as I have seen, the pinkish varieties of T. porosa are confined to the eastern half of the world. Even the ridges and crests on the under side of the scutum vary in some degree; and the tergum in T. porosa varies considerably, and in some of the other species, slightly, in general shape: I believe that the tergum becomes narrow and elongated, when the shell is steeply conical, with the orifice of small diameter. After having spent several days in disarticulating and closely examining the many specimens of T. porosa in my possession, I concluded that its varieties formed at least four species, these being in external appearance extremely distinct; but ultimately the many intermediate forms compelled me to unite all into a single species. Again, I may instance the conical, ribbed variety of T. purpurascens (Pl. 11, fig. 1 b), with the outer lamina of the shell preserved and with the radii widely developed, as having not the smallest resemblance to the other common depressed variety (fig. 1 a), having a granulated surface, produced by the exposed tips of the upfilled parietal tubes, and without a trace of the radii or even of the sutures; I may add that, according to the characters used by some authors, these two varieties would be classed in two separate genera.

To distinguish the species of this genus, the chief reliance must be placed (as in the case of most other sessile cirripedes) on the general outline of the opercular valves, and on the ridges and crests on their under sides: the internal structure, however, of the radii, and in a lesser degree of the parietes, must not be overlooked. I have not found the parts of the mouth, or the differences in the cirri, of much service; and it will be shown under T. porosa, that the

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relative numbers of the segments in the several cirri, and even their shape, is extraordinarily variable.

Affinities.—All the species are pretty closely allied, and there is no ground for making any sectional division of the eight species, more especially not on the ground whether or no the radii are developed. Tetraclita purpurascens, taking into account all the characters, including the animal's body, is perhaps the most distinct species in the genus, but it is closely allied to T. costata. In the well-marked character of the parietes being formed of a single row of large tubes, T. rosea differs from all the other species. The genus is closely allied to Balanus; I can point out no difference in the animal's body, nor any constant difference in the opercular valves. The ridges and crests on the under sides of the scuta are more prominent in Tetraclita; and all the species, excepting two, have crests (though sometimes very slight) for the attachment of the rostral depressor muscle, and these occur only in two species of Balanus: crests, also, for the attachment of the lateral depressor muscle are common in Tetraclita, but rare in Balanus. The main character, however, of the genus, as compared with Balanus, is derived from the existence of only four compartments, and in a lesser degree from the several rows of parietal pores; but, as just stated, T. rosea has only a single row, and, on the other hand, in Balanus crenatus, there is a slight tendency exhibited, in the dividing of the longitudinal septa near the outer lamina, to form a second row of parietal pores; and in B. cariosus, moreover, we actually have two or three rows of irregular and very short pores. The thin, yet solid calcareous basis which occurs in all the species of Tetraclita, excepting T. purpurascens, resembles the basis in Balanus flosculus and imperator, but I suspect that the structure of the cement-ducts is different in the two genera.

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1. TETRACLITA POROSA. Pl. 10, fig. 1 a-1 m.

LEPAS POROSA. Gmelin. Syst. Naturæ, 1789.*

BALANUS SQUAMOSUS. Bruguière. Encyclop. Method., 1789, Pl. 165, fig. 9, 10.

LEPAS FUNGITES. Spengler. Skrivter af Naturhist. Selskabet, 1 B., 1790.

— POROSA. Wood's General Conchology, Pl. 9, fig. 4, 1815.

TETRACLITA SQUAMULOSA. Schumacher. Essai d'un Nouveau Syst., &c., 1817.

BALANUS STALACTIFERUS. Lamarck. Animaux sans Vertèbres, 1818.

— — Chenu. Illust. Conch., Pl. 4, fig. 6, 7.

ASEMUS POROSUS. Ranzani. Memoire di Storia Naturale, Tab. 3, fig. 32-35.

CONIA POROSA. Sowerby. Genera of Recent and Fossil Shells, Plate, 1823.

— — Leach. (sine descript.) Encyclop. Brit. Supplement, vol. 3, 1824, Tab. 57.

Radii rarely present, when present narrow; even the sutures often absent: shell steeply conical, with the surface generally corroded, and having a stalactiferous appearance.

Var. (1) communis (Pl. 10, fig. 1 a): outer lamina of shell almost wholly removed; the portion preserved, as well as the exposed parietal tubes, gray, or pale dirty brown, or dull purple.

Var. (2) nigrescens (Pl. 10, fig. 1 c): outer lamina of shell almost wholly removed; the portion preserved, and the exposed parietal tubes, very dark purple or inky black.

Var. (3) viridis; outer lamina of shell almost wholly removed; the portion preserved, and the exposed parietal tubes, green; under surface of opercular valves clouded green.

Var. (4) rubescens (Pl. 10, fig. 1 b): outer lamina of shell almost wholly removed; the portion preserved, and the exposed parietal tubes, pale reddish-purple, or peach-blossom purple; under surfaces of opercular valves often reddish purple; terga often rather narrow, with the spur somewhat pointed, and with the basal margin on the carinal side sloping, or not making an angle with the spur.

—————————————————————————————————————————————

* As Gmelin and Bruguière published the same year, I do not know which comes first, but I have adopted the best known name. Most authors give, amongst their references, Chemnitz, vol. 8, Tab. 98, fig. 836, 837, but the accompanying description is more applicable to T. serrata of this work than to T. porosa; without a figure or description, however, of the under side of the scutum it is impossible to decide. Several authors, also, give Lepas cariosa of Pallas, as a synonym; this, however, is the Balanus cariosus of this work.

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Var. (5) elegans (Pl. 10, fig. 1 d): outer lamina preserved, excepting sometimes near the summit of the shell; white, tinged with yellowish brown from the epidermis; surface strongly ribbed longitudinally; orifice rather small; sheath reddish-purple; terga narrow, with the basal margin sloping as in var. rubescens.

Var. (6) communis (young) (Pl. 10, fig. 1 e): radii developed, very narrow; outer lamina of shell preserved, gray or dull purple; surface slightly ribbed longitudinally.

Var. (7) patellaris (Pl. 10, fig. 1 f ): radii developed, very narrow, white; outer lumina of shell preserved, generally reddish-purple; steeply conical, with the orifice extremely small; surface smooth, with longitudinal white ribs. Terga very narrow, with the spur sharply pointed, and with the basal margin on the carinal side sloping towards it, or not making an angle with it. Scuta, with the adductor ridge very prominent. Attached to a ship's bottom.

Hab.—West Indies, Brazil, West Colombia, Panama, Galapagos Archipelago, California, Philippine Archipelago, China, East coast of Australia, Red Sea; generally attached to tidal rocks, sometimes to shells, sometimes to wooden posts. Very common.

General Appearance.—This, the widest-distributed and much the commonest species of the genus, varies greatly in external appearance. The usual shape is steeply conical, but some individuals are much depressed. In the common varieties the outer lamina of shell has been removed even close to the basal edge; the upfilled parietal tubes being thus exposed (fig. 1 b), as flattened adpressed points. These points are largest in large specimens, but they vary somewhat in size in specimens of equal growth. When the outer surface is preserved, it is generally ribbed longitudinally, but is sometimes quite smooth. The most general colour is dirty gray or dark purple; but many specimens are pale pinkish-purple, owing to the exposure of the parietal tubes upfilled with shelly matter of this tint: there are also, as given under the characters of the vars., black, white and green varieties. The sheath is always tinted by the prevailing colour. The radii are rarely developed, but generally the four sutures are distinct; sometimes these are externally quite obliterated, the shell, as seen from the outside, consisting of a single piece like a patella or fissurella. When the radii are developed they are very narrow, with their upper edges oblique: their development seems always coincident with the more or less perfect preservation of the shell, and their function is to enlarge the orifice; the enlargement being usually effected by the disintegration and removal of the whole upper part of the conical shell. The size of the orifice varies considerably; in the seventh variety it was extraordinarily small; in outline it varies from oval to rounded trigonal or rhomboidal; in some specimens, with the radii well developed, it was rounded pentagonal.

Size.Tetraclita porosa is the largest species of the genus; I have seen specimens attached to a large pebble of granite in the British Museum, which measured two inches in basal diameter, and nearly one inch and a half in height.

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Scuta: these are sub-triangular and generally a little elongated, but they vary slightly in relative breadth (fig. 1 i, 1 l), and likewise in the degree to which the basi-tergal angle is rounded off. The under surface is clouded with dull or pinkish-purple, or with green, or is nearly white. The articular ridge is not prominent, and the articular furrow is narrow. The adductor ridge is prominent, and runs upwards for some distance close and parallel to the articular ridge; and sometimes it extends nearly or quite up to the apex of the valve; in one single specimen the adductor ridge had an abraded appearance, and was very little developed. The crests for the rostral and lateral depressores are sharp and distinct. Along the occludent margin, the ends generally of the alternate lines of growth are enlarged into knobs, serving to lock the two valves together; but in many specimens only two or three knobs, at intervals of several lines of growth (fig. 1 b), are developed.

Terga: when the upper end of the valve is not corroded, there is a distinct beak, hollow within for a thread of corium. The scutal margin is not much inflected, and the articular ridge not very prominent. The spur is placed quite close to the basi-scutal angle of the valve, so that there is no basal margin on that side of the valve. Te width of the valve and of the spur, and the acumination of the extremity of the latter, varies in a remarkable manner. In the broad and commonest variety (fig. 1 k), the basal margin of the valve form an angle of about 130° with the carinal side of the spur, and the basal end of the spur is broad and truncated. In the less common and narrow variety (1 m), the basal margin in some extreme cases forms very nearly a straight line with the carinal side of the spur; and the spur itself is bluntly pointed: in var. 7 it is sharply pointed.

Structure of the parietes and radii.—In all cases the four sutures are quite distinct, from top to bottom, on the internal lamina of the shell, and generally they run through the whole thickness of the walls, and are visible externally. Often they do not quite reach the outer lamina, and then the shell externally consists of a single piece, like a patella. Sometimes the sutures can be traced running through the parietal tubes only for a short distance from the internal surface; where they cease, the two walls of the suture become fused together. When a perfect suture is split open, the radius is represented (fig. 1 h) by a few narrow, sinuous ridges, sending out on each side little branches or denticuli; these are received into corresponding furrows in the opposed compartment. These ridges run nearly parallel to each other, and somewhat obliquely, from the outer lamina of the shell to the basis. When the radii are developed, their edges are similarly formed, by sinuous denticulated ridges, with the interspaces between them filled up solidly. The alæ are but little prominent.

The mouth does not deviate from the generic type. The cirri are remarkable from the variability in the several pairs of the relative numbers of their segments, as shown in the following table. The segments do not correspond even on opposite sides of the same individual, as may be seen in the two lower lines of the table. I believe that variability to this degree is very uncommon in other cirripedes, though, as stated in the Introduction, the number of the segments always increases with

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the growth of the individual. The terminal segments in the longer rami of both the first and third cirrus are antenniformed,—being elongated, and of a different shape, with fewer bristles, compared with the basal segments of the same cirri. It is apparently these terminal segments which are particularly liable to vary in number. In both rami of the third cirrus, some of the segments, from the sixth to the eleventh inclusive, (counting from the bottom), more especially the eighth, ninth, and tenth, carry a few spines coarsely and doubly pectinated; but as some of the adjoining segments carry spines which may be called doubly serrated, it is not easy to draw an exact line of demarcation. Sometimes, though rarely, a few of the nearly terminal segments in the second cirrus are furnished with similar, doubly pectinated spines.

Numbers of the segments in the rami of the Cirri, in different specimens.

  First cirrus. Second cirrus. Third cirrus Sixth cirrus.

Shorter ramus. Longer ramus. Shorter ramus. Longer ramus. Shorter ramus. Longer ramus. Either ramus.
Specimen from Pernambuco, Brazil (var. 1) . . . 9
19
10
11
15
27
26
Another specimen from the same cluster (var. 1) . 12
23
12
14
14
19
23
From the Galapagos Archipelago, (var. 1) . . . 10
16
10
11 ?
11
16
25
From the Philippine Archipelago, (var. 4) 10
?
10
10 11 19 18
From California (var. 5) . 15
24
22
From the bottom of a ship (var. 7), young . . . 9
9
10
17
14
From South America (var. 1) British Museum . . .
11
18
11
12
13
21
22
Another specimen from the same cluster with the last specimen . . . . 16
25
13
18
15
23
27
Same individual, but the cirri from the opposite side of the body 15
28
15
21
16
23

Varieties.—Under the generic description, I have stated that after having spent some time in examining a very large suite of specimens of T. porosa, I concluded that at least four of the varieties were true species. It so happened that all the specimens which I first examined of the var. (4) rubescens, had the narrow sloping terga, and scuta with only two or three great teeth on their occludent margins; but ultimately, in a group thus characterised, I found one or two individuals with terga precisely of the shape of those in var. (1) communis. Again, in a group of dull purple specimens of var. communis, a few had the narrow sloping terga, and scuta with teeth on their occludent margins, intermediate in size and number between the varieties with only one or two

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great teeth, and those with every alternate growth-ridge enlarged into a tooth. Hence var. rubescens completely broke down as a species.

With respect to var. (5) elegans (a M.S. specific name of Leach) I inferred at first, from external appearance alone, that it was distinct; the outer lamina of the shell and even the epidermis is preserved; the surface is strongly ribbed, and the whole shell, excepting the sheath, is nearly white; the terga are narrow, with a sloping basal margin as in var. (4) rubescens. Whole groups of specimens are thus characterised. But as var. communis is often white, and as the surface, when the outer lamina is preserved, is generally, as we shall presently see, ribbed longitudinally, the differences in var. elegans are quite unimportant.

The (6th) var. differs from var. communis only in the narrow radii having been developed, and consequently in the orifice being pentagonal, and in the outer, longitudinally ribbed lamina of the shell having been preserved. In the same group of specimens, I have seen every intermediate stage between this and the common form. It must not, however, be supposed that the young of var. communis always pass through these stages, for such is not the case. In the genus Balanus it has been seen, how capricious in some species is the development of the radii.

Of the other varieties, enumerated at the beginning, no further mention is required, excepting with respect to var. (7), the most singular of all. I have seen only three specimens, sent to me by Dr. Aug. Gould, of Boston, United States, and these from the appearance of their bases I have no doubt had been attached to a ship,—the only instance which I have met with, in the present species. The shell is steeply conical, with the orifice so small as to be reduced to a mere pore; the radii are extremely narrow and white; the shell is thin, with the surface smooth, but ribbed longitudinally and regularly; the outer lamina of the shell and the epidermis are perfectly preserved; the upper part of the shell is reddish purple, which dies away towards the base: careful examination of the apex shows that at the first growth the young shell was blueish-green. The terga are narrow, with a sloping basal margin, as in var. rubescens, but with the point of the spur sharper. I have formerly remarked that the shape of the terga seems influenced by the size of the orifice. The lower edge of the sheath depends freely: I have seen no other instance of this latter structure, so common, but so variable, in Balanus, in the present species, except to a partial extent in one distorted specimen, in Mr. Stutchbury's collection, adhering to Balanus tintinnabulum, and probably taken from a ship's bottom. I may add that this distorted specimen was remarkable from its radii being wider than in any other instance,—from its smooth uncoloured surface without longitudinal ribs,—and from the perfect preservation of the epidermis over its entire surface. Although Dr. Gould's specimens, in external aspect, are absolutely and entirely different from the common varieties of T. porosa, there are so many intermediate forms, and the differences are so little important that I feel no hesitation in attributing them to variation, consequent on the individuals having been exposed to unusual conditions, attached to the bottom of a ship.

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2. TETRACLITA SERRATA. Pl. 10, fig. 2 a-2 d.

Shell dark greenish-gray, with narrow, longitudinal, serrated ribs: radii absent: scutum with the adductor and articular ridges forming a cavity, which runs up to the apex of the valve.

Hab.—Cape of Good Hope; Algoa Bay; attached to sandstone and to Patellæ; Mus. Brit., Cuming, and Stutchbury.*

General Appearance.—Colour dark greenish gray; form steeply conical; surface covered, especially in the lower half of the shell, by numerous, narrow, sharp, longitudinal ridges, but slightly prominent, and serrated or transversely divided into small teeth: when the shell has been much disintegrated, the upper part of the surface consists of the exposed, smooth, rather large, upfilled parietal tubes. I have seen no instance of the development of the radii; sometimes even the sutures are with great difficulty distinguishable, though I believe they always reach the outer surface; sometimes the sutures are wide from the disintegration of the edges of the compartments. Orifice rounded or oval.

Scuta.—The scuta and carinal half of the terga are blueish-green. In the scuta neither the articular ridge or furrow are much developed: the adductor ridge is prominent, and is united to the articular ridge, about half way up the latter, thus forming a rather large, triangular cavity, which runs up the apex of the valve.

The Terga are beaked. The spur, measured across the upper part, is half as wide as the valve; it is bluntly pointed; it is placed quite close to the basi-scutal angle of the valve, so that there is no basal margin on that side; it curves towards the scutum, its extremity extending beyond the basi-scutal angle.

Structure of the Shell and Radii.—The parietal tubes are rather large, especially those adjoining the inner lamina of the walls. The shell is of singularly little specific gravity, which is due to the parietal tubes not being filled up with shelly matter nearly to so great an extent as in the other species; even in the uppermost part the tubes are not solidly filled up, only their external sides are thickly coated with greenish-black shell, which by corrosion becomes grayish. The radii, as stated, are not developed: the shell breaks with singular facility along the sutures, and the radii are then seen to be most feebly represented

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* I have seen three separate lots of this species all from the Cape of Good Hope; one lot was collected by Dr. Krauss, at Algoa Bay, and I strongly suspect is the species described by him in his 'Südafrikanischen Mollusken' as Conia porosa. If the species, figured by Chemnitz, and mentioned in a note (p. 329), under T. porosa, be the present species, the specimens probably did not come from Tranquebar, on which point Chemnitz speaks only from memory. I have seen one specimen ticketed New South Wales, it is possible, considering the case of T. rosea, that this may be correct, but I should like to have further confirmation before giving it as a habitat.

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by a few very small branching ridges. The alæ have their edges plainly crenated. The sheath is dark green, with the lower edge free.

The Mouth presents no particular characters. With regard to the Cirri, I am doubtful whether any confidence can be placed in the numbers of the segments being constant; but I may state that the second cirrus contained thirteen and sixteen segments in its two rami; the third cirrus only fourteen in both rami; and the sixth cirrus twenty-six segments in both rami. Whereas in every specimen of T. porosa, the longer ramus of the third cirrus contained more segments than either ramus of the second. About half the segments, namely, those in the middle of both rami of the third cirrus, are furnished with coarsely and doubly pectinated spines, like those in T. porosa.

Affinities.—Upon the whole, this species is more nearly allied to T. porosa than to any other. In the cavity formed by the union of the adductor and articular ridges, it is allied to T. cœrulescens. This species differs from all, in its little specific gravity, consequent on the parietal tubes being only slightly filled up, and in the peculiarly serrated, narrow, approximate ridges on the external surface of the walls. The character derived from the adductor ridge, just alluded to, is remarkable. In the shape of the terga, in the absence of radii, and in the structure of the body, this species approaches closely to T. porosa.

3. TETRACLITA ROSEA. Pl. 10, fig. 3 a-3 d.

CONIA ROSEA.* Krauss. (!) Die Sudafrikanischen Mollusken, Tab. 6, fig. 28, 1848.

BALANUS CUMINGII. Chenu. Illust. Conch., Tab. 4, fig. 5.

Shell dirty white, tinged with pink; parietes formed by a single row of large tubes; radii generally narrow: tergum with the spur rather short and broad.

Hab.—New South Wales, Moreton Bay in lat. 27°, Port Jackson, and Twofold Bay; South Africa, Algoa Bay. Attached, in Australia, to littoral rocks and shells; often associated with T. purpurascens, Chthamalus antennatus, and Catophragmus polymerus; Mus. Brit., Cuming, Krauss, Darwin, Stutchbury.

General Appearance:—Shell steeply conical, often rather convex; dirty or brownish white, feebly tinted with pink; external surface generally much disintegrated, and having in the upper part a pillared appearance, owing to the exposure of the upfilled, large, square, parietal

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* I am greatly indebted to Professor Krauss for having sent me, for examination, the unique specimen collected by himself in Algoa Bay. There can be no doubt of the identity of the African and Australian specimens. It is a singular circumstance that the same species should occur in these two distant places, and, as far as at present known, not in the intermediate, more tropical coasts.

[page] 336

tubes, and, in the lower part, a striated (and sometimes serrated) appearance, from the exposure of the parallel, approximate plates, with which the outer lamina of the shell is internally strengthened. In only a few young specimens, the whole outer lamina of the shell was well preserved; and in these the surface was very smooth, and even glossy, giving to the specimens a quite different aspect; even in partially corroded specimens, the lower part of the shell sometimes is quite smooth. Generally, the radii are developed; in most specimens they are narrow, but sometimes of moderate width; their summits are oblique, and their edges often notched or toothed. The recipient furrow, in each opposed compartment, is often almost as wide as the radius itself, and is equally notched. In some much corroded specimens there were no radii. Basal diameter of largest specimen, 1.1 of an inch.

Scuta, generally thick, sometimes very thick, with the external surface usually much corroded: articular furrow rather wide; articular ridge not very prominent; adductor ridge prominent. The rostral depressor muscle is attached in a small oblong pit, sometimes including little crests; and the lateral depressor muscle is attached to what may be described either as three or four parallel furrows or crests.

Terga, with the spur placed close to the basi-scutal angle, so that there is no basal margin on that side; spur short, with its lower end truncated and rounded; broad, even exceeding, when measured across the upper part, half the width of the valve. Articular furrow wide. Apex not beaked.

Structure of Walls and Radii.—This species differs from all the others of the genus in having only a single row (fig. 3 d) of parietal tubes; these are large, quadrangular, but elongated in the ray of the circle. They are not filled up, even at the very top of the shell, but they become thickly lined all round with compact shelly matter. When the surface of the shell is disintegrated, these upfilled tubes greatly affect, as already stated, the external appearance. The outer lamina near the basis is internally strengthened by longitudinal, sharp, approximate ridges or plates, which, also, often affect, after corrosion, the external appearance. The radii have their sutural edges formed by a set of narrow, branching ridges or septa; the ends of which, seen externally, often give a notched outline to this edge; the recipient furrows in the opposed compartments are deep, and their edges likewise are often notched: the interspaces between the branching ridges are filled up solidly. The alæ have their edges coarsely crenated. The lower edge of the sheath is not free.

The mouth and cirri present no particular characters: the third cirrus has both its rami elongated, with the terminal segment tapering. In the three posterior pairs of cirri, the tufts of little spines between the main pairs are rather large.

Affinities.—This species has no particular affinity with any other. The circumstance of there being only a single row of parietal tubes is not so important a difference as might at first be thought, inasmuch as in the other species, during their quite early youth, the walls are formed of only a single row of tubes or pores.

[page] 337

4. TETRACLITA PURPURASCENS. Pl. 11, fig. 1 a-1 d.

LEPAS PURPURASCENS.* Wood's General Conchology, p. 55, Pl. 9, fig. 42, 1815.

BALANUS PLICATUS. Lamarck. Animaux sans Vertèbres, 1818.

— — ET PUNCTURATUS. Chenu. Illust. Conch., Tab. 4, fig. 3 et 12.

CONIA DEPRESSA (!) J. E. Gray. Appendix, Dieffenbach's Travels in New Zealand, 1843 (sine descript. vel figurâ).

Shell depressed, pale purple or dirty white, with the surface longitudinally ribbed, or corroded and granulated: radii or even sutures none, or radii well developed and broad, with their summits parallel to the basis: basis membranous: scutum transversely elongated: tergum small, with the spur extremely short and rounded.

Hab.—Sydney, New South Wales; Flinder's Lagoon, Sir C. Hardy's Island, Barrier Reef; King George's Sound, Western Australia; Van Diemen's Land; New Zealand, adhering to Pollicipes spinosus; Mus. Brit., Cuming, Stutchbury, Darwin, &c. China (?) attached to Pollicipes mitella, Mus. Brit. and Stutchbury. Generally attached to tidal rocks, sometimes to shells. Very common.

General Appearance.—Shell generally much depressed, in a few cases rather steeply conical, in one single instance cylindrical, but not much elongated. Colour, when alive, pale, but fine purple; I presume, judging from some dryed specimens, sometimes dirty white. The state of the surface varies remarkably: about half the specimens (fig. 1 a) which I have seen, had the outer lamina of shell quite removed, and the surface granulated, owing to the projecting and exposed tips of the upfilled parietal tubes; the radii are not developed, and often even there is no trace of the four sutures; the rather large orifice is somewhat rounded, and the two scuta, with their surfaces disintegrated, have their middle parts deeply indenting the terga. The shell, in the other and perhaps more common condition (fig. 1 b), has the outer lamina preserved, and is longitudinally ribbed with generally at least five or six ribs on each compartment: the radii are here very wide, and extend from tip to tip of the compartments, so that their summits are parallel to the basis; they are gene-

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* The descriptions given by Wood and Lamarck are fuller and more accurate than is usual in the case of Cirripedes, and I have no doubt regarding these two names. The Conia depressa of Dr. J. E. Gray is, as I know from having seen the original specimens, the young of this same species; the name is unaccompanied by any description or figure.

22                           

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rally covered by a brownish epidermis, thickly clothed with little spines; the orifice is neatly diamond-shaped; the apices of the opercular valves meet at a common point: these specimens are almost always smaller and younger than the granulated specimens. Altogether the specimens in the two opposite states have, in their external appearance, nothing in common, and no one, without careful examination, would ever suspect that they were specifically identical; this, however, was proved by the intermediate forms, and, in one instance, three of the compartments had their surfaces granulated, and were entirely destitute of the radii, whilst the fourth by some chance had been preserved from corrosion, was longitudinally ribbed, and had its epidermis-covered radius fully developed. The difference in the appearance of the opercular valves, in the two states, is simply owing to the degradation of their upper parts in the granulated specimens.

The basal diameter of the largest specimen was one inch, but the height only .35 of an inch.

Scuta, transversely elongated, so that the basal margin is nearly twice as long as the tergal margin: articular ridge very little prominent; articular furrow wide but shallow; adductor ridge very blunt, slightly prominent, sometimes almost absent, almost parallel to the basal margin: there are no distinct crests for the rostral or lateral depressores muscles, but some small irregular pits for the latter. In one young specimen, the lines of growth were crenated, showing a tendency in the valve to become longitudinally striated, as in the allied T. costata. In some young and immature specimens, the basal margin was deeply sinuous.

Terga, small in area, not above half that of the scuta: spur extremely short, broad, placed close to the basi-scutal angle of the valve, so that there is no basal margin on that side of the spur. The lower end and sides of the spur form one uniform curve. Articular ridge barely developed. Crests for the tergal depressores sharp and prominent.

Structure of the Shell and Radii.—The walls are very thick, and the parietal tubes small and numerous; there are sometimes from twelve to fifteen rows of tubes in the thickness of the wall. The tubes in their whole upper part are filled up solidly; and, as we have seen, are often exposed by disintegration. In very young specimens, of that size in which in T. porosa there would be only a single row of parietal tubes, there were here two or three rows. The development of the radii, as we have seen, is very capricious; the sutures even sometimes being lost. The radii, when developed, are broad, square on the summit, and covered by brownish hirsute epidermis: internally they are formed of tubes like those forming the parieties; in this respect differing from all the species except the following, T. costata. The tubes in the radii run obliquely down towards the basis; instead of in a transverse line, directly towards the opposite compartment, as might have been expected from the structure of the radii in Balanus. The alæ have their edges finely crenated. The sheath in all the specimens which I have observed is colourless; its lower edge is not free. The corium entering the parietal tubes, and lining the opercular valves, the mouth, and the anterior cirri, is generally of an extremely dark purple colour.

[page] 339

The Basis is entirely membranous, in which respect this species differs from all the others in the genus.

Mouth: all the trophi are unusually hairy or spinose. The labrum is deeply notched and apparently destitute of teeth on the crest. The palpi are club-shaped or enlarged at their extremities. The mandibles have the fourth tooth rudimentary.

In the Cirri, the second and third pairs are remarkably short and blunt. In one specimen the two rami of the first cirrus had respectively six and sixteen segments; those of the second, six and seven; those of the third, seven and seven; and those of the sixth cirrus twenty rather elongated segments, with a small tuft of spines between each main pair of spines.

Affinities.—This species differs from all, in its membranous basis, and in its transversely elongated scuta. It resembles T. costata, and differs from all the other species, in its radii (when developed) being square on the summit, and in being formed of tubes,—in the smallness and number of the parietal tubes,—in the absence of crests on the under side of the scuta for the rostral and lateral depressor muscles,—in the shortness and rounded form of the spur to the terga,—and, lastly, in the club-shaped palpi and small size or absence of the fourth tooth in the mandibles. T. purpurascens differs from T. costata in those points, namely, in its membranous basis and transversely elongated scuta, in which it differs from all the other species, and, moreover, in its scuta not being plainly striated longitudinally, in having more ribs on the external surface of the parietes of its shell, and in having only three pairs of main spines on the three posterior cirri.

5. TETRACLITA COSTATA. Pl. 11, fig. 2 a-2 c.

Shell depressed, whitish, generally with ten very prominent longitudinal ribs: radii broad, with their summits parallel to the basis: basis calcareous: scutum externally striated longitudinally: tergum with the spur short and rounded.

Hab.—Philippine Archipelago, Mus. Cuming. Attached to various shells, within the tidal limit.

General Appearance.—Shell whitish, probably tinged, when alive, with reddish-purple; depressed; surface perfectly preserved, smooth, but having longitudinal very prominent ribs, almost invariably ten in number; namely, three on both the rostrum and carina, and two on the two lateral compartments, with ten corresponding projections round the basal margin. Orifice passing from rounded-trigonal to diamond-shaped. The radii are very broad and square at the summit, and extend from tip to tip of the compartments. Basal diameter of largest specimen under half an inch, generally from .3 to .4 of an inch.

[page] 340

Scuta, of the usual sub-triangular, and not transversely elongated, as in T. purpurascens. External surface striated longitudinally; in many specimens there is a medial depression, or a row of very small pits, such as occur on the scuta of Balanus trigonus and lævis. The adductor ridge is moderately developed, and runs nearly parallel to the occludent margin; there are no crests for the rostral and lateral depressor muscles.

Terga: these in area equal two thirds of the scuta: the spur is short and rounded, and placed as described under T. purpurascens; but the articular ridge seems to be more prominent than in that species.

Structure of the Shell and Radii.—The parietal tubes are small, and very numerous, as in T. purpurascens. The radii are wide, square on the summits, but not so conspicuously covered by hirsute epidermis as in that species. Internally, the tubes forming the radii are smaller, and run more transversely than in T. purpurascens, that is in the normal course, as in Balanus. The edges of the alæ are nearly or quite smooth. The Basis is as distinctly calcareous, as in the other species of the genus.

Mouth: the trophi are not so hairy as in T. purpurascens; the labrum seems destitute of teeth; the palpi are club-shaped at their ends; the mandibles have only three teeth. The second and third cirri are not so short and blunt relatively to the others as in T. purpurascens. In the posterior cirri, the elongated segments carry four main pairs of spines, between which there is no intermediate tuft of fine spines.

The Affinities of this species have been fully pointed out under the last and closely related species. In external appearance, T. costata can at first hardly be distinguished from those young and pale-coloured varieties of T. purpurascens, which have their external surface not corroded, and their radii well developed.

6. TETRACLITA VITIATA. Pl. 11, fig. 3 a-3 e.

Shell white, generally tinged in the upper part with pink; surface irregular: parietal tubes very irregular: radii moderately wide, with their summits oblique: alæ with very thick crenated sutural edges: tergum with the spur not joined to the basi-scutal angle; spur with its extremity equably rounded.

Hab.—Philippine Archipelago; Barrier Reef, (Raine's Islet), Australia; Mus. Cuming and Stutchbury. Attached to massive corals, to coral-rock, to a Tridacna, and to Tetraclita cœrulescens.

General Appearance.—Shell conical, moderately steep: white, generally with a tinge of pinkish-purple in the upper part, owing to the

[page] 341

exposure of the tips of the upfilled parietal tubes. The lower part of the surface is generally well preserved, and is formed by very irregular, branching, longitudinal, slightly prominent, ridges. Radii of moderate width, with their summits oblique. Orifice rather large, rounded trigonal.

Scuta, rather narrow, with the upper part acuminated: the external surface generally much disintegrated, and marked with some irregular blotches of dark red. Articular ridge not prominent; articular furrow rather deep: adductor ridge, distinct from the articular ridge, pretty well developed, as are the crests for the rostral and lateral depressor muscles. In young and well preserved scuta, there is an external, medial, hyaline band, corresponding with the hollow under the adductor ridge, and caused by the thinness of the valve along this line.

Terga: externally, the carinal half is longitudinally and very feebly striated. Internally, the articular furrow is very wide, but shallow, and of unusual length, owing to the preservation of the upper part of the valve; the articular ridge is not prominent. The spur does not actually join, as in all the foregoing species, the basi-scutal angle, but is separated from it by a short piece of basal margin; its two sides are more nearly parallel than is usual, and the end is regularly rounded. It is always rather narrow, though the width varies considerably (fig. 3 d, 3 e). It extends in the same straight line with the middle of the articular furrow. The terga, though not possessing any striking characters, differ considerably in appearance from those of the other species.

Structure of the Shell and Radii.—The parietal tubes are remarkable from their irregular shapes, and unequal sizes (fig. 3 b),—hardly two resembling each other. Sometimes a single elongated tube will reach across the whole thickness of the walls. The septa between the tubes are rather thick and rugged. The tubes are generally darkly coloured from the adhering corium; they are solidly upfilled, but only in the uppermost part, by dark chocolate-red shelly matter. The radii are formed by irregularly branching ridges, with the interspaces filled up solidly. The square edges of the alæ are much thicker than in any other species, and are furnished with transverse ridges, which are sometimes slightly branched. The inner lamina of the walls near the basis, in most of the specimens, is irregularly and longitudinally ribbed, the ribs being longitudinally striated. The sheath and the upper part of the inner lamina of the parietes are clouded with chocolate-red.

The animal's Mouth and Cirri were ill-preserved; but I was able to make out that the labrum had some strong teeth, and that the mandibles were furnished with five teeth, a greater number than in any other species. The palpi had parallel sides as usual. In the sixth cirrus, the segments had four pairs of main spines, instead of the usual number of three.

Affinities.—This species does not appear to be particularly related to any other one: perhaps it is rather nearer to the two following than to the foregoing species. The irregular parietal tubes, thick-edged alæ, form of terga, five teeth to the mandibles, and four pairs of spines to the segments of the posterior cirri, are its chief characteristics.

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7. TETRACLITA CŒRULESCENS. Pl. 11, fig. 4 a-4 d.

LEPAS CŒRULESCENS. Spengler. Skrivter af Selskabet, 1 Bind., 1790.*

Shell with the upper part tinged greenish-blue, longitudinally ribbed: radii moderately wide, with their summits oblique: scutum with a small adductor and extremely prominent articular ridge, united together and so forming a small sub-cylindrical cavity: tergum with the spur not joined to the basi-scutal angle.

Hab.—Philippine Archipelago, attached to Balanus tintinnabulum; attached to a ship's bottom, and to Balanus tintinnabulum, both from the Pacific Ocean; attached to a massive coral, and associated with T. vitiata, and therefore from the tropical eastern seas; Mus. Brit., Cuming, Stutchbury.

General Appearance.—Shell conical, sometimes depressed; surface with rather broad, smooth, longitudinal ridges; whitish, with the upper part greenish-blue, sometimes very feebly tinted with pink; radii white, or mottled with blueish-green, or with pink. When the outer lamina of shell has been corroded, the upfilled parietal tubes, of a dull blueish-gray colour, are exposed. The radii are moderately wide, with their summits very oblique. In basal diameter, one specimen was 1.8, and another 1.5 of an inch.

Scuta, externally furrowed very slightly in a longitudinal direction, causing the lines of growth to become a little sinuous. The valve is strong and thick; and the epidermis, when preserved, is hirsute with spines. The articular ridge is extraordinarily prominent; it projects, as measured from the external surface of the valve, to an amount equalling half the width of the valve in its widest part. The adductor ridge is very short, and is united to the bottom of the articular ridge, thus forming a small, nearly cylindrical tube, which runs up to near the apex of the valve. The inflected occludent margin is broad and coarsely toothed. The crests for both depressor muscles are not very prominent. When the scuta and terga are articulated together, owing to the great projection of the articular ridge of the scutum, its upper part is separated from the tergum (fig. 4 b), by a remarkably wide and deep,

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* The longitudinally folded walls, as described by Spengler, the blue colour, the habitat, namely, associated with B. tintinnabulum from the East Indies, and more especially the expression "Valvulæ operculi cardine dentato mobilis," apparently referring to the highly prominent articular ridge of the scutum, leave little doubt on my mind that I have rightly named the present species.

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fissure-like hollow. The scutum, in some distorted specimens from a ship's bottom, was narrow in proportion to its ordinary breadth.

Terga.—These are large. Externally, there is a broad, longitudinal depression, bounded on each side by a ridge. The carinal half is feebly striated longitudinally. A large upper portion (fig. 4 b) projects freely, and stands, when the two valves are articulated together, above the apex of the scutum, but does not form a beak as in T. porosa. Internally, the tergal margin is widely inflected: the articular furrow is very deep, but the articular ridge is not prominent. The spur is not very broad; it is separated from the basi-scutal angle by a small space of basal margin, which forms a straight line with the basal margin on the opposite side of the spur. The end of the spur is truncated, and is parallel to the basal margin.

Structure of the Shell and Radii.—The walls are thick: the parietal tubes are rather large and regular; they become solidly filled up in their upper parts. The sutural edges of the radii are formed by unusually narrow, sinuous ridges, sending off delicate denticuli on each side: the interspaces between these ridges are solidly filled up. The crenated edges of the alæ are rather thick. Neither the mouth nor the cirri offer any noticeable character; but I may observe, that, in the mandibles, the third and fourth teeth are close together; and that, in the three posterior cirri, the tufts of small spines between the main pairs are small.

Affinities.—This species is very distinct from the others, with the exception of the following T. radiata, to which it is in several respects allied. The under side of the scutum, with its great articular ridge, and the cylindrical tube formed by the union of the latter with the short adductor ridge, affords the most noticeable character.

8. TETRACLITA RADIATA. Pl. 11, fig. 5 a-5 d.

CONIA RADIATA.* De Blainville. Dict. Sc. Nat., 1816-1830, Pl. 164, fig. 5, 5 a, (sine descript.)

— LYONSII. G. B. Sowerby. Genera of Recent and Fossil Shells, Plate, 1823, (sine descript.)

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* The synonymy of this species is complicated. De Blainville gives no description under the article Conia, published in 1818, or in the vol. published in 1822; but I believe, from the figures of the opercular valves, that I have correctly identified this species with his C. radiata. Mr. Sowerby gives no description of C. Lyonsii, or any figure of the opercular valves, but his drawing of the shell is much better than de Blainville's, and I believe it is the same species. Whether de Blainville's or Sowerby's plate appeared first I cannot ascertain. In the second edition of Lamarck, Conia radiata of Blainville is given as a synonym to Balanus radiatus of that work; but this is quite erroneous. I may add that if de Blainville's name does not apply to the present species, it must to T. cœrulescens, and as the latter is the older name it will be

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Shell white, with numerous approximate longitudinal ribs: radii broad, with their summits slightly oblique, internally porose: tergum with the articular ridge extraordinarily prominent, with the spur not joined to the basi-scutal angle.

Hab.—West Indies, adhering to Balanus eburneus and to Lepas anserifera. New South Wales, adhering to Tetraclita porosa. Attached to Balanus tintinnabulum, on a ship's bottom from Sumatra; not rarely attached to Balanus tintinnabulum on ships' bottoms; Mus. Brit., Stutchbury, and Cuming.

General Appearance.—Shell white, rather steeply conical, with numerous, approximate, rather narrow, longitudinal, rounded ribs on the walls: in a specimen half an inch in diameter, there were from eight to twelve ribs on each compartment. The outer lamina of shell seems always well preserved. Orifice rounded, trigonal. Radii white, smooth, broad, with their summits only slightly oblique. I have seen one specimen 1.2 in basal diameter, but quarter of an inch is a common size, and very young specimens are unusually frequent in collections.

Scuta broad, externally not striated longitudinally. The articular ridge is prominent, and the furrow deep, but not in so great a degree as in T. cœrulescens. The adductor ridge is only slightly prominent; it extends upwards only a little way above the lower end of the articular ridge, and does not form with the latter a cavity. There are no crests for the rostral depressor muscle, but there is a little pit, formed by the folding over of the occludent margin.

Terga.—These valves, when articulated with the scuta (fig. 5 b), project above them to an extraordinary degree, and are separated from them by a deep, fissure-like hollow, caused by the remarkable prominence of the articular ridge of the terga. The upper part of the tergum is not beaked, and does not project freely much above the sack. The valve is large; externally there is a rounded longitudinal furrow. The tergal margin is broadly inflected. The articular furrow is deep, and the articular ridge far more prominent than in any other sessile cirripede, for it projects, as measured from the outside surface, more than half the width of the valve; and consequently the valve, when viewed vertically from above, almost appears as if formed by the union of three plates, viz., the articular ridge, and the outside surface on each side of the spur. The spur is of moderate width, with the corners rounded: it is placed near, but not close to the basi-scutal angle, so that there is on this side a small portion of basal margin,

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permanent. In this case, T. radiata might be allowed to stand as my own name, considering that Mr. Sowerby's figure is imperfect and is not accompanied by any description. At first I thought that the present species might be the Lepas mitra of Spengler, ('Skrivter af Naturhist. Selskabet,' 1790, Tab. 6, fig. 5), but the parieties are not described as porose; and the folds on the walls are too broad; on the other hand, his description of the opercular valves makes me think this may be the same species.

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forming nearly a straight line with the margin on the carinal side. In some young specimens, about the tenth of an inch in diameter, from the West Indies and from New South Wales, the spur (the position of which I found varied a little in some other specimens) was placed nearly in the middle of the valve, and very nearly at right angles to the basal margin; it is possible that these may be a distinct species, but without larger specimens to judge from, I think it more probable that this difference in the tergum is due to variation and youth.

Structure of Shell and Radii.—The parietal tubes are commonly elongated in the ray of the circle: the septa are rather thick, and strongly crenated at their basal edges. The inner lamina of the walls is strongly ribbed longitudinally. The broad radii have their sutural edges formed by ridges, with numerous and closely approximate denticuli: the interspaces between the main ridges are not soon filled up, and at the bottom, each interspace usually terminates in a pore or tube; so that the radii are not solid, as in most of the foregoing species, but porose. The alæ have their edges crenated.

Basis, calcareous, of unusual thickness; the inner, or upper surface, is striated from the centre in rays, corresponding with the ribs on the inner lamina of the walls. This striated or furrowed structure in the basis, shows a tendency to its becoming tubular or porose, as may be inferred from analogous cases in Balanus.

Animal's body unknown.

Affinities.—This species is rather more closely allied to the last than to any other. There is a close analogy in the peculiar manner in which the scuta and terga are articulated together in the two species: in this species it is effected by the great development of the articular ridge of the tergum, and in T. cœrulescens by that of the scutum. The internally striated calcareous basis, and the internal tubular interspaces between the denticulated ridges of the radii, are peculiar characters. The white colour, the narrowly and closely ribbed parietes, and the broad radii, give this species an aspect, by which it can be easily recognised.

4. Genus—ELMINIUS.

ELMINIUS. Leach. Zoological Journal, vol. 2, July, 1825.

Compartments four: parietes not porose.