AMMONITES — ZOOLOGICAL, ETC, 



317 



do not leave any doubt as to their application, when criti- 

 cally made, and with a perfect knowledge of the species. 



It remains for me to explain how some species may be 

 found in a group superior to the one of which they are cha- 

 racteristic, in order to remove all doubts which may be 

 raised respecting them. 



Ammonites were doubtless pelagic animals, living in the 

 bosom of the ocean, probably in the same manner as the 

 Nautilus, from which they differed, notwithstanding, by seve- 

 ral internal characters, and chiefly by the divisions of the 

 posterior edge of the mantle ; but they possessed this cha- 

 racter in common with the Nautilus, that in proportion as 

 they increased in size, to compensate for the weight ac- 

 quired by the animal, the latter filled a fresh chamber with 

 air by means of a septum, so as to restore its equilibrium, 

 as I have already mentioned when describing the zoological 

 characters. Hence it follows, that on the death of the 

 animal, the shell, having the chambers filled with air, would 

 not sink to the bottom ; but would be transported on the 

 surface of the water by the winds and currents, in the same 

 way as the shells of Nautilus and Spirula, and consequently 

 cast on shore. This property which the shell possesses of 

 floating, explains two questions : the one zoological, the 

 other geological. 



The first consists in the opinion that living Ammonites 

 may yet exist in the present seas, I shall answer this by 

 the single fact of the nature of the shell. If Ammonites 

 existed at present, as the shell could not sink to the bottom 

 of the sea in consequence of the air which it contains, it 

 would unquestionably be cast on some coast or other, in the 

 same manner as the Nautili and Spirulee, and it could not 

 have escaped the numberless collectors of shells, who have 

 been spread over the surface of the globe for so many ages. 

 We must renounce, then, for ever the hope of finding a living 

 Ammonite. 



