around themselves in the form of a winding tower, gradually diminishing towards the apex (Pl. 44, Fig. 14.)[1]
The same essential characters and functions pervade the Turrilites, which we have been tracing in the Scaphites, Hamites, Baculites, and Ammonites. In each of these genera it is the exterior form of the shell that is principally varied, whilst the interior is similarly constructed in all of them, to act as a float, subservient to the movements of Cephalopodous Mollusks. We have seen that the Ammonites, beginning with the Transition strata, appear in all formations, until the termination of the Chalk, whilst the Hamites and Scaphites are very rare, and the Turrilites and Baculites do not appear at all, until the commencement of the Cretaceous formations. Having thus suddenly appeared, they became as suddenly extinct at the same period with the Ammonites, yielding up their place and office in the economy of nature to a lower order of Carnivorous mollusks in the Tertiary and existing seas.
In the review we have taken of genera in the family of Chambered shells, allied to Nautilus, and Ammonite, we have traced a connected series of delicate and nicely adjusted instruments, adapted to peculiar uses in the economy of every animal to which they were attached. These all attest undeviating Unity of design, pervading many varied adaptations of the same principle; and afford cumulative evidence, not only of the exercise of Intelligence, but also of the same Intelligence through every period of time, in which these extinct races inhabited the ancient deep.
- ↑ The shells of the Turrilites are extremely thin, and their exterior is adorned and strengthened (like that of Ammonites,) with ribs and tubercles. In all other respects also, except the manner in which they are coiled up, they resemble Ammonites; their interior being divided into numerous chambers by transverse plates, which are foliated at their edges, and pierced by a siphuncle, near the dorsal margin. (Pl. 44, Fig. 14, a, a.) The outer chamber is large.
