INTRODUCTION. 



Of the Animals inhabiting Shells. 



The animals inhabiting shells, belong to the Class 

 Mollusca, and are divided into two orders; viz. 

 those with an appendage, or foot, proper for creep- 

 ing, and a distinct head, Gasthopodes ; and those 

 which have no foot, or one that is not calculated for 

 creeping, and are without a head, AcSphales. The 

 animals of both divisions are quite soft, that is, 

 without bones or any internal hardness, and form 

 a considerable portion of Lamarck's work, entitled 

 Animaux sans vertebres. 



The GastSropodes, or those with the climbing or 

 creeping foot, are confined to univalve shells ; while 

 those without a head, called AcSphales, chiefly in- 

 habit the bivalves. As to the animals of multivalve 

 shells, some are headless, and others have a peculiar 

 organization, (such as the Lepades) which is inde- 

 pendent of the rest. 



The head, of such of these animals as have one, 

 vol. i. a 



