Lamarck's Genera of Shells. 71 



crawling on the bottom, or along the shores, by the assistance of 

 their arms. Most of the latter conceal themselves amongst the 

 rocks. They are all carnivorous, and prey on crabs and other 

 marine animals. The position of their arms admirably facilitates 

 the conveyance of the food to the mouth, whose strong mandibles 

 serve to crush the hard bodies which the animal seizes on. Some 

 of the cephalopoda are quite naked, others inhabit a thin, unilo- 

 cular shell which envelopes them, and which they can cause to 

 float on the surface of the water : others, again, are provided with a 

 multilocular shell, either wholly, or in part internal. 



These latter are very numerous, and singularly diversified in 

 regard to form ; the ocean, especially at great depths, seems filled 

 with them, so great is the multitude of fossil multilocular shells, 

 met with in the older formations. With the exception of some 

 species of a pretty large size, the greater part of these shells are 

 extremely minute. 



The shells of those cephalopoda which are furnished with them 

 afford but little instruction from their form, as to that of the ani- 

 mals which produced them. To distinguish these shells we can 

 only compare them with one another ; and we are as yet ignorant 

 whether the divisions we may thus establish, will coincide with the 

 principal divisions we should form of the mollusca themselves, if 

 we had the opportunity of being better acquainted with them. 



The multilocular shells of this order, are extremely remarkable 

 from their diversity of form, and have hitherto greatly embarrassed 

 naturalists in their attempts to determine the relation of the animals 

 which produce them, to the known conchiferous mollusca. The 

 manner in which these shells were formed, their connexion with the 

 animal, whether it inhabit the last chamber of the shell, be wholly, 

 or only in part contained in it, or whether the shell be more or less 

 completely internal, were all questions which we had no means of 

 determining, till MM. Sueur and Peron, brought the animal of 

 the spirula from New Holland. This animal is a true cephalopoda, 

 and has a multilocular shell inserted in the posterior part of its 

 body, only a portion of the shell being visible ; hence we may con- 

 fidently presume that all multilocular shells, or those which are 



