| ↑ 1 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| Still more recently, a Pyrgoma, a member of a distinct sub-family of sessile cirripedes, has been discovered by Mr. Woodward in the upper chalk; so that we now have abundant evidence of the existence of this group of animals during the secondary period.
|
|
| → in 1859 1860 1861 1866 1869 |
| according to Agassiz, in 1872 |
|
|
in the oldest tertiary beds; from the ease with which even a fragment of a valve can be recognised; from all these circumstances, I inferred
had sessile cirripedes existed during the secondary periods, they would certainly have been preserved and discovered; and as not one species had
discovered in beds of this age, I concluded that this great group had been suddenly developed at the commencement of the tertiary series. This was a sore trouble to me, adding as I
one more instance of the abrupt appearance of a great group of species. But my work had hardly been published, when a skilful palæontologist, M. Bosquet, sent me a drawing of a perfect specimen of an unmistakeable sessile cirripede, which he had himself extracted from the chalk of Belgium. And, as if to make the case as striking as possible, this
cirripede was a Chthamalus, a very common, large, and ubiquitous genus, of which not one
has as yet been found even in any tertiary stratum. ↑
Hence we now positively know that sessile cirripedes existed during the secondary period; and these cirripedes might have been the progenitors of our many tertiary and existing species. |
|
| The case most frequently insisted on by palæontologists of the apparently sudden appearance of a whole group of species, is that of the teleostean fishes, low
→in
the Chalk period. This group includes the large majority of existing species. Lately, Professor Pictet has carried their existence one sub-stage further back; and some palæontologists believe that certain much older fishes, of which the affinities are as yet imperfectly known, are really teleostean. Assuming, however, that the whole of them did appear, as Agassiz
at the commencement of the chalk formation, the fact would certainly be highly remarkable; but I
|
