MOLLUSCA. 39 



relle de Paris. These papers, with some additional obser- 

 vations, were at last published in a separate form, under the 

 title Memoires pour servir a Vhistoire et a V Anatomic des 

 Mollusques, Paris, 1816. In the following year he published 

 Le Regne Animal, distribue d'apres son organisation, in 

 which he arranged the mollusca according to his peculiar 

 views, from characters drawn exclusively from the animal. 

 In the third volume, of what may be termed the third edi- 

 tion of that invaluable work, published in 1830, the same 

 arrangement, with the exception of a few modifications, was 

 adhered to. 



He divides the mollusca into six classes, which he terms 

 Cephalopoda, Pteropoda, Gasteropoda, Acephala, Brachi- 

 opoda, and Cirrhipoda. 



In the class CEPHALOPODA, the body is in the form of a 

 sack, open above, containing the branchiae, with a distinct 

 head, surrounded by fleshy elongations or arms, adapted for 

 moving the body or seizing prey. Into this class, along with 

 the Sepia of Linnaeus, Cuvier has inserted the multilocular 

 shells of his genus Nautilus and the genus Argonauta. But 

 it is to be feared, that our knowledge of the testaceous mol- 

 lusca which inhabit the numerous multilocular shells, is too 

 limited to enable us to assign to all of them their true place 

 in a natural arrangement of animals. 



In the second class, termed PTEROPODA, the body is 

 closed, the head is destitute of the long fleshy arms which 

 distinguish the animals of the preceding division; two fin- 

 like membranes, situate on the sides of the neck, and on 

 which the branchial tissue is in general spread, serve as or- 

 gans of motion. There is only one shelly mollusca belong- 

 ing to this class, viz., the anomia tridentata of Forskaehl, 

 now forming a part of the genus Hyaloea. 



