274 Report on Organic Remains. 



mens of the recent Nautilus, a multilocular shell resembling 

 the Ammonite, but with the exception of a figure given by 

 Rumphius, which was generally considered as apocryphal, 

 nothing was known respecting the animal inhabiting the shell. 

 The voyage of Peron and Lesueur, furnished many speci- 

 mens of the Nautilus spirula, L. Gm. now the Spirula australis, 

 another multilocular shell. Many of these shells contained 

 the living animal, which was ascertained to belong to the true 

 cephalopodal mollusca. The animal resides in the last cham- 

 ber, or rather the sides of the shell are imbedded in its body. 

 Lamarck supposes that in the N. pompilius, a distinct line 

 within, shows how far this last chamber is imbedded in the 

 body of the animal. By means of a siphunculus, which is 

 partly calcareous and partly membranous, a communication 

 is established between the animal and all the chambers of 

 the shell. The use of the chamber seems to be intended 

 to counteract the increasing weight of the shell; and the 

 siphunculus, admitting air or other gaseous products at the 

 will of the animal, would necessarily alter and vary its spe- 

 cific gravitjr, for the purposes of locomotion. This will 

 serve to explain the organization not only of the Ammonites, 

 but also of the Orthocerites, Belemnites, Baculites, and all 

 other multilocular shells. 



The species of Ammonites have not as yet been well studied 

 and arranged ; and it is some what remarkable, that the simple 

 and clear division proposed by Professor Wahlenberg, in the 

 Transactions of the Royal Society of Sweden, has not been 

 generally adopted.* 



Professor Wahlenberg divides all Ammonites into two 

 classes, founded on the arrangement of the septa, or partitions 

 between the chambers. 



* We have not had an opportunity of consulting the rncent labors of 

 M. D'Orbigny, on this class of mollusca, contained in the Aunales det Sc. 

 Nalurelles, 



