35 



GENERIC SYSTEM. 



We come now to the anangement of Shells, after 

 the method of Linnaeus ; and if we bear in mind 

 the professed foundation of that arrangement, we 

 shall find but Httle cause to comjilain, either of per- 

 plexity in the general scheme, or of want of pre- 

 cision in the several descriptive parts. It is upon 

 external characters, upon those of the testaceous 

 covering, and not upon the genus or species of the 

 worm, that we are to erect our system ; because 

 the former are the most obvious, and the least liable 

 to misconception. 



Premising, then, that by the word Vhlve is 

 meant auy single piece of calcareous substance, let 

 the form be what it may, which serves as a habi- 

 tation, or protection, either partially or entirely, 

 to a Molluscous animal, we shall understand the 

 iiatural divivsion of all shells intoMultivalves, those 

 d2 



