146 
faintly in the recurved part. This seemed to manifest that, at different 
periods of its growth, the animal had undergone such certain changes, 
in the organization of those parts on which the formation of its shell 
depended, as fitted them for depositing the shell in this intended pe- 
culiar form. It is true, that although the tubercles might not be per- 
ceptible in the first whirls, yet as the size of the animal increased, so 
would the respective parts which formed the shell ; and, of course, so 
would the tubercles also, whether the shell was extended in a spiral 
or a lengthened form. But under the supposition that this had been 
the case, and that these were the labours of the animal of the Cornu 
ammonis, which had erroneously, as it were, continued out its shell 
in this, instead of the spiral form, still the parts of the shell would have 
continued increasing in size with the animal. But here the reverse 
takes place ; for, after the animal has made its reflected turn, the 
nodules begin to lessen, and the whole of the shell is formed on a 
diminished scale ; from which we may safely infer, that a change of 
organization in these parts, appropriate to the different changes of 
form in the shell took place naturally in the animal, and affords suffi- 
cient reason for considering it as forming a genus from that of 
Ammonites. 
This is confirmed by the chalk fossil, Plate X. Fig. 11, which, with 
several others, was found by my friend, Mr. Herbert, in a chalk-pit 
near Brighton. Although but little of this shell appeared, and no more 
could be traced into the chalk, I was satisfied, when I first saw it, that 
it could not belong to the genus Ammonites ; and, as several were 
found in the same pit, there was no reason for supposing that its pe- 
culiar formation was the result of accident. Comparison with the 
preceding fossil, which I have since obtained, shows plainly that it is 
of the same genus, and perhaps of the same species, with it. 
LXXXI. Turrilites. A spiral, turriculated, multilocular shell, the 
turns contiguous, and all visible. The chambers divided by sinuous 
septa, pierced in their disks. The mouth round. 
