^ INTRODUCTION. 



Testaceous animals iiiliallt their shells, to which 

 they are only partially attached ; whereas the 

 Crustacea are indued with theirs, each limb being 

 invested with its own peculiar shield. 



Shells are either terrestrial, or found in rivers, 

 lakes, in shallows of the sea, or in the deeper beds 

 of the ocean; they are, however, all subject to the 

 same arrangement, according to their generic and 

 specific characters, and not according to their in- 

 dividual locality. 



On the physiology of testaceous on'imals, which 

 belong to a distinct Order, that of Mollusca in the 

 Class Vermes, it will not be expected that much 

 should be said in a ifiere elementary treatise. Still 

 onlv half the object would be attained, if it were 

 totally silent on a subject so fraught with wonder, 

 so indicative of the wisdom and the Providence 

 which first produced these little admirable archi- 

 tects, and instructed them to form their beauteous 

 receptacles. Ahich as we delight in viewing the 

 delicate and brilliant tones of colour, the sym- 

 metrical structure, or the picturesque and rugged 

 surface which distinguish the different families of 



