TURRiLiTE :3G9 
It is remarkable that those approximations 
to the structure of Ammonites which are pre- 
sented by Scaphites and Hamites, should have 
appeared but very rarely, and this in the lias 
and inferior oolite,* until the period of the cre- 
taceous formations, when the entire type of the 
ancient and long continued genus Ammonite 
was about to become extinct. 
Turrilite, 
The last genus I shall mention, allied to the 
family of Ammonites, is composed of spiral shells, 
of another form, coiled around themselves in the 
form of a winding tower, gradually diminishing 
towards the apex (PL 44, Fig. 14). f 
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 
* The Scaphites bifiircatus occurs in the Lias of Wurtemburg, 
and Hamites annulatus in the Inferior oolite of France. 
f 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 trans- 
verse plates, which are foliated at their edges, and pierced by a 
siphuncle, near the dorsal margin. (PI. 44, Fig. 14, a, a.) The 
outer chamber is large. 
GEOL. B B 
