“Now, although certain genera, such as Terebratula, Rhynchonella, Crania, and Discina, have enjoyed a very considerable geological existence, there are genera, such as Stringocephalus, Uncites, Porambonites, Koninckina, and several others, which made their appearance very suddenly and without any warning; after a while they disappeared in a similar abrupt manner, having enjoyed a comparatively short existence. They are all possessed of such marked and distinctive internal characters that we cannot trace between them and associated or synchronous genera any evidence of their being either modifications of one or the other, or of being the result of descent with modification. Therefore, although far from denying the possibility or probability of the correctness of the Darwinian theory, I could not conscientiously affirm that the Brachiopoda, as far as I am at present acquainted with them, would be of much service in proving it. The subject is worthy of the continued and serious attention of every well-informed man of science. The sublime Creator of the universe has bestowed on him a thinking mind; therefore all that can be discovered is legitimate. Science has this advantage, that it is continually on the advance, and is ever ready to correct its errors when fresh light or new discoveries make such necessary.” The late Joachim Barrande, the great palæontologist of Bohemia, bears similar testimony.
Fig. 61.—Group of Older Palæozoic Lamellibranchs.—After Billings.
1, Cucullea opima. 2, Nucula oblonga. 3, Nucula lineata. 4, Cypricardia truncata. 5, Tellina ovata. 6, Nucula bellatula. 7, Modiola concentrica.
The ordinary bivalves, like the mussels and cockles, now so very plentiful on our coasts, are rare in the Cambrian and Silurian, and for the first time make a somewhat conspicuous appearance in the Upper Silurian and Devonian. But from the first they resemble very closely their modern successors, though on the whole neither so large nor so ornate ([Fig. 61]). Their fortunes have thus been precisely the opposite of those of the Brachiopods, though in neither case is there very marked elevation or deterioration in the individual animals. A very similar statement may be made as to the sea-snails, whether the curious winged snails (Pteropods) or the ordinary crawlers (Gastropods). The former come in early, and are represented by Palæozoic forms finer than any now extant. The genus Conularia ([Fig. 62]) presents some Silurian species six inches or more in length, which are giants in comparison with any now living. The forms of more ordinary Gastropods from the Silurian represented in [Fig. 63] will suffice to show that their styles are not very dissimilar from those still extant.[17] As in the case of the ordinary bivalves, however, the modern Gastropods much exceed in numbers and magnitude those of the Palæozoic.
Fig. 62.—Conularia planicostata (Dn.). A Carboniferous Pteropod.