2 
INTRODUCTION. 
Testaceous animals inhabit 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 
individual locality. 
On the physiology of testaceous animals, 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 mere elementary treatise. Still, 
only 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. Much 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 
