146 



riods of its growth, the animal had undergone such certain changes, in 

 the organization of those parts on which the formation of its shell de- 

 pended, as fitted them for depositing the shell in this intended peculiar 

 form. It is true, that although the tubercles might not be perceptible 

 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 erro- 

 neously, 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 ani- 

 mal 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 sufficient reason for considering it as forming a genus 

 distinct 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 peculiar for- 

 mation was the result of accident. Comparison with the preceding fos- 

 sil, 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. 



Langius gives the figures of two fragments of two distinct species of 

 this fossil ; one of which he describes, Turbinites striatus striis transversis 



