RECORD: Stephens, James Francis. 1833. Description of Chiasognathus Grantii a new lucanideous insect forming the type of an undescribed Genus, together with some brief remarks upon its structure and affinities. Transactions of the Cambridge Philosophical Society 4: 209–17.

REVISION HISTORY: Transcribed (single key) by AEL Data 3.2013. RN1

NOTE: This work formed part of the Beagle library. The Beagle Library project has been generously supported by a Singapore Ministry of Education Academic Research Fund Tier 1 grant and Charles Darwin University and the Charles Darwin University Foundation, Northern Territory, Australia.


[page 209]

VI. Description of Chiasognathus Grantii, a new Lucanideous Insect forming the type of an undescribed Genus, together with some brief Remarks upon its Structure and Affinities. In a Letter addressed to one of the Secretaries.

BY J. F. STEPHENS, ESQ. F.L.S.

[Read May 16, 1831.]

MY DEAR HENSLOW,

THE magnificent Beetle submitted by you to my inspection proves to be, as I anticipated, not only perfectly novel to science as a species, but forms the type of a genus as interesting from its structure, as it is remarkable for its splendour and colouring. I shall therefore very briefly notice some of its peculiarities, though I cannot but regret that from the circumstance of my attention having been chiefly directed to indigenous entomology, the task should have devolved upon one so little conversant with exotic forms, and more especially as Great Britain is remarkably deficient in the group to which the present insect belongs.

The Lucanidæ, to which family Chiasognathus appertains, are distinguished amongst other characters by the extraordinary developement of the mandibles in the males, which in the common Stag-beetle rarely exceed half the length of the body,

Vol. IV. Part II. D D

[page] 210

but in Chiasognathus they acquire an elongation exceeding that of the body; they are extremely strong and robust at the base, and evidently capable of biting very sharply; towards the middle they become flattened, and at the tips they are incurved so as to cross over each other—whence the origin of the name I have applied to the genus*—the internal edge is irregularly serrated throughout, with a large tooth towards the base, and the apex has an acute recurved hook (Plate X. Fig. 4). In the genus Lucanus a small tubercle may be observed at the outer base of each mandible; in the insect now under examination this is greatly developed, and forms an acute spinous process about one-third the length of the mandibles, serrated within, and pointing inwards, so that in situ the two cross each other towards the apex similarly to the mandibles themselves.

The upper lip (labrum,) is very distinct, being composed of a coriaceous plate with a strong rib down the centre.

The lower jaws (maxillæ, Plate IX. Fig. 4.) are small, but the apical portion is very long and delicate, and fringed with very slender hairs:—the maxillary palpi are elongate, slender, with the basal joint very short, the second nearly as long as the others united, sub-clavate, the third half the length of the second, the terminal elongate, somewhat attenuated.

The lower lip (labium, Pl. IX. Fig. 8.) is membranaceous, with two, rather broad, flat, elongate, laciniæ, the extreme edge of which is finely ciliated:—the labial palpi are short, with the basal joint very short, the second rather longer, the terminal one nearly as long as the other two united, and attenuated.

* Xιαζω decusso, Pναθоѕ maxilla.

[page] 211

The mentum (Pl. IX. Figs. 5. and 7.) is transverse, semicircular, and notched anteriorly.

The Antennæ are remarkable for the extraordinary elongation of the basal joint and the whorl of hairs which ornament its tip; the remaining joints are short, the three first somewhat obconic, the two following transverse and produced within, the four terminal ones also produced within; the process being longer, and the articulations more distinctly laminated.

The furcate anterior portion of the head (clypeus), and above all, the distinct existence of four eyes, as well as the great strength of the fore legs, are characters of no little importance: to which may be added the superb colours with which nearly the entire insect is adorned; the castaneous golden-bronze of the elytra, the burnished golden-green of the gibbous centre of the thorax, and the iridescent hues of its sides and of its posterior spines, form an assemblage of intense tints rarely united into one form. In fact every part of this unique insect possesses characters of extreme interest, as may be clearly perceived through the medium of the accompanying figures, executed by my friend Mr. Westwood, who in his delineations observed several peculiarities which he kindly pointed out to me.

The food of the Lucanidæ consists of the flowing sap of decaying trees, which in the typical genus is lapped up by the four plates or laciniæ of the maxillæ and lower lip; but in this insect the very arched form of the mandibles appears to form an obstacle to the application of the laminæ to the tree unless the mandibles be opened to a great extent, as may be readily seen by the lateral view (Pl. X. Fig. 3.) given in the accompanying figure.

Respecting the affinities of this insect, the genus which makes the nearest approach to it is evidently Pholidotus, with which it

D D 2

[page] 212

somewhat agrees in the structure of its maxillæ and of the inferior portion of the trophi, excepting that the mentum is glabrous; the genus above mentioned is manifestly allied to Lamprima, and these two genera with Chiasognathus contain the only Lucanideous insects (with the exception of Platycerus) that are adorned with metallic colours. In Lamprima the maxillæ are short; the basal joint of the antennæ shorter than the remainder taken together; the mandibles slightly elongated; but in Pholidotus the maxillæ are elongated, being furnished with a penicilliform process as in Lucanus, the three apical joints of the clava of the antennæ are alone enlarged, and the basal joint is longer than the remainder, the mandibles are large, clothed with down on their inner surface, and the mesosternum is slightly produced in front as in Lamprima. Chiasognathus therefore, by varying from the above allied genera in several of these particulars, makes a near approach to Lucanus, which is the only genus of the group containing species which may vie with it in bulk, strength of mandibles, habit, and general conformation; hence it evidently forms a truly beautiful and interesting link between the two conterminous genera Lucanus and Pholidotus, or the two families Lucanidæ and Lamprimidæ, possessing the gigantic structure of the former, and the resplendent hues of the latter family.

[page] 213

CHIASOGNATHUS.

Antennæ fractæ, articulo primo longissimo, sub-flexuoso, gracili, ad apicem incrassato et fasciculo pilorum instructo, clavâ pectinatâ, sex-lamellatâ, articulis quatuor ultimis subæqualibus.

Labrum distinctum, subcoriaceum, carinatum.

Mandibulæ longissimæ, intus serratæ, apice incurvæ et decussatæ, basi incrassatæ, subtus processu spiniformi, intus serrato, armatæ.

Maxillæ processu apicali longissimo, exserto, gracili, subattenuato, pilis brevibus instructo.

Palpi maxillares elongati, graciles, articulo primo brevissimo, secundo longissimo, sub-clavato, tertio dimidio breviore, ultimo elongato, subattenuato.

Labium membranaceum, laciniis duabus, sub-latis, elongatis, armatum.

Palpi labiales breves, articulo primo brevi, secundo longiore, tertio longissimo, attenuato.

Mentum transversum, semicirculare, natice emarginatum.

Corpus depressiusculum, sub-latum. Caput latum, transversum, sub-triangulare; clypeo furcato emarginato, versus latera utrinque subspinoso. Oculi quatuor, convexi. Thorax truncato-conicus, antice in medio rotundatus et pone oculos excisus, lateribus dilatatis, deflexis, ad angulum posticum profundè emarginatis, spinis duabus acutis armatis, basi bisinuato. Scutellum rotundatum. Pedes elongati, femoribus anticis magnis, sub-cylindricis, sub-glabris, intermediis et posticis gracilioribus, tenuè pilosis, marginibus anterioribus et posterioribus densè

[page] 214

ciliatis; tibiis anticis elongatis compressis, apice emarginato, externé sub-convexis, interné sub-planis, versus apicem paulò curvatis, prope marginem anticum spinis acutis armatis, extus multidentatis, dentis duobus apicalibus magnis; intermediis et posticis brevioribus, teretibus, apice interno bicalcarato, extus serratis; tarsi articulis quatuor basalibus sub-æqualibus, ultimo elongato clavato, unguiculis duabus compressis, acutis, curvatis.

SP. 1. Grantii. Sub-viridi-aureus, cupreo refulgens, thorace gibbo viridi intense, lateribus angulisque posticis versicoloribus, elytris subcastaneo-tinctis, femoribus aureo-viridibus, tibiis cupreo-ferrugineis, tarsis antennisque nigris, abdominis segmentorum marginibus testaceis, pectore lanugine griseo tecto. (Longitudo corporis ♂ 3 inc. 3½ lin.).

In honorem Di. Geo. Grant, M. D. hoc splendidissimum insectum nominavi.

DESCRIPTION.

Mandibles (of the male) rather more than half the length of the body, finely but distantly punctured, with a few longitudinal wrinkles at the base, the inferior process very glossy and impunctate, colour rich copper, tinted with brilliant shades of a golden hue, the base and its appendage rich blue-green and iridescent; the curvatures bronzed-black; head bright golden-green, varying in tint with the light, the disc very glossy, remotely, but finely, punctate, bluish; the lateral and posterior margins of a variable golden hue, with the spinous processes of

[page] 215

the clypeus purplish bronze: eyes glaucous: thorax unequal, truncate-conic, with the anterior margin rounded in the middle, and gradually excised on each side behind the eyes, the anterior lateral angle acute; the lateral margins dilated and deflexed, with a deep impunctate fovea on each, and the hinder angle with a profound circular excision terminating in two spines, of which the posterior one is longest; the base is laminated; the disc gibbous, rugose-punctate anteriorly, very glossy and impunctate posteriorly, and produced into an abbreviated ridge, composed of two lunules; the colour is intense golden-green, with the anterior and posterior margins rich purplish-copper, varying in certain positions of light to blue and violet, especially towards the posterior angles, and the foveæ on the lateral margin are fine purplish-green; scutellum of this last tint, impunctate, its base clothed with short pale hairs in the centre; elytra very finely granulated throughout, except the humeral elevation, which is smooth, of a greenish-chesnut, with a coppery or golden hue, the suture, apex, and a narrow indeterminate streak towards the lateral margin somewhat ferruginous, the lateral margin itself and the reflexed portion of the elytra bright green with iridescent tinges. Beneath: the sides of the head are bright green, slightly iridescent, and regulose-punctate, the palpi and throat black, the latter impunctate, the mentum deep violet; breast purplish-copper, slightly punctate on the sides, with a few transverse wrinkles between the anterior legs: abdomen, anteriorly, or rather post-pectus, densely clothed with pale lutescent hairs, the remaining portion bluish-green, slightly pilose, with the margins of the segments pale testaceous: femora finely pubescent above, glabrous beneath, the four hinder ones producing a dense fringe of pale hairs anteriorly and posteriorly, all of a bright bluish-

[page] 216

green, tinted with coppery above; tibiæ above coppery-green, with a tendency to castaneous, beneath rusty-chesnut, tinged in certain directions of light with greenish; the serrations, tubercular processes, and spines at the apex purplish-black; tarsi brown- black; antennæ the same; with the singular fascicle of hair at the apex of the basal joint pale griseous. At the base of the mandibles exteriorly, and on the sides of the thorax are a few very short pale scattered hairs, and on the ridge which divides the eyes is a long delicate fringe of similarly coloured ones; the anterior and posterior margins of the thorax both above and below are also densely ciliated with short pale hairs.

The female is unknown, but in all probability, when discovered, the mandibles will be found to be abbreviated, and the form of the clypeus and thorax slightly different from those of the male.

I am, Your's, &c.

J. F. STEPHENS.

P. S. Dr. GRANT, the gentleman who presented this interesting specimen to the Society, was surgeon on board H. M. S. Forte, when she returned to England in the summer of 1830, from the South American station. The Insect was brought to him in January by a native, who stated that he had found it on a resinous shrubby plant in the Island of Chiloe, which is separated from the Main Land at Valparaiso by a very narrow channel.—It appeared to have been a recent capture.

[page] 217

EXPLANATION OF THE PLATES.

Plate Fig.
IX. 1. CHIASOGNATHUS GRANTII, under side.
2.
3. Maxillæ with lacinia and palpus.
4.
5. Mentum, processes of labium and palpi, under view.
6. Base of anterior femora.
7. Mentum, labium, &c. upper view.
8. Labium with processes and palpi, lateral view.
X. 1. CHIASOGNATHUS GRANTII, upper view.
2. Mandibles, head, thorax, &c.
3. Lateral view of ditto.
4. Apex of mandibles.
5. Antennæ.
6. Tarsus.

Vol. IV. Part II. EK

[plate ix]

[plate x]


This document has been accessed 961 times

Return to homepage

Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)

File last updated 27 February, 2014