COLLECTION OF SHELLS. 5o5 



several animals of this class have only an interior 

 shell, and others have none at all, the affinity of 

 their organization does not admit of their being 

 separated. 



The animals belonging to certain shells are 

 preserved in spirits of wine ; those of a large 

 size, as also the naked mollusca, are placed at 

 the bottom of the third division of the chest of 

 drawers, immediately after the collection of 

 insects. 



In going through the collection we shall fol- 

 low the order adopted by M. de Lamarck; 

 deviating only by proceeding from the most 

 complicated animals to those which are more 

 simple. 



The mollusca naturally form two divisions. 

 The first comprehends the univalves, or those 

 whose shell is formed of only one piece, and of 

 some analogous genera without shells. The se- 

 cond comprehends the bivalves, or those whose 

 shells consist of two pieces, There are aquatic 

 and terrestrial species belonging to the first divi- 

 sion, but all those of the second are aquatic. 



The univalve mollusca are divided into five 

 orders ; the heteropoda, the cephalopoda, the tra- 

 chelipoda, the gasteropoda, and the pteropoda. 



The order heteropoda consists of the single 

 genus carinaria. The most celebrated species 



