the latter appearing, for the first time, after the total annihilation of many species and genera of a more complex character.[1]
The prodigious number, variety, and beauty, of extinct Chambered shells, which prevail throughout the Transition and Secondary strata, render it imperative that we should seek for evidence in living nature, of the character and habits of the creatures by which they were formed, and of the office they held in the ancient economy of the animal world. Such evidence we may expect to find in those inhabitants of the present sea, whose shells most nearly resemble the 'extinct fossils under consideration, namely, in the existing Nautilus Pompilius, (See Pl. 31, Fig. 1,) and Spirula, (Pl. 44 Figs. 1, 2.)[2]
- ↑ The introduction, in the Tertiary periods, of a class of animals of lower organization, viz. the carnivorous Trachelipods, (See Chap. XV. Section 1,) to fill the place which, during the Secondary periods, had been occupied by a higher order, namely, the carnivorous Cephalopods, affords an example of Retrocession which seems fatal to that doctrine of regular Progression, which is most insisted on by those who are unwilling to admit the repeated interferences of Creative power, in adjusting the successive changes that animal life has undergone.
It will appear, on examination of the shells of fossil Nautili, that they have retained, through strata of all ages, their aboriginal simplicity of structure; a structure which remains fundamentally the same in the Nautilus Pompilius of our existing seas, as it was in the earliest fossil species that we find in the Transition strata. Meantime the cognate family of Ammonites, whose shells were more elaborately, constructed than those of Nautili, commenced their existence at the same early period with them in the Transition strata, and became extinct at the termination of the Secondary formations. Other examples of later creations of genera and species, followed by their periodical and total extinction, before, or at the same time with the cessation of the Ammonites, are afforded by those cognate Multilocular shells, namely, the Hamite, Turrilite, Scaphite, Baculite, and Belemnite, respecting each of which I shall presently notice a few particulars.
- ↑ I omit to mention the more familiar shell of the Argonauta or Paper Nautilus, because, not being a chambered species, it does not apply so directly to my present subject; and also, because doubts still exist whe-
