MOLLUSCA. 13 



however, are terrestrial; and some appear to live almost constant- 

 ly under ground, such as the Testacellcc, but this is rare. A 

 great number are found on the surface, such as the Limaces, 

 Helices, &c. ; while some are to a certain degree amphibious, 

 as the Lymncece. By far the greater part, however, live in wa- 

 ter, fresh and salt. Of the fresh water kinds some remain free 

 at the surface of the mud, others adhere to other bodies. Of 

 the latter, the circumstances in this respect are considerably va- 

 ried. Some are found only on the coasts, and are termed lit- 

 toral species, as the genera Patella, Turbo, &c. ; others appear 

 to exist only at a distance from the shores and in deep water, 

 whence they are called Pelagic species ; and the Sepiaria wan- 

 der in the depths of the ocean. 



With respect to their geographical distribution little is known, 

 this subject not having been submitted to sufficient investiga- 

 tion. They are found, however, in all parts of the world, whe- 

 ther in the seas, rivers, and lakes, or on land. Certain tribes 

 are confined to particular zones, while others appear to inhabit 

 all. Thus the Sepiaria occur in all seas, while the Nautilus 

 and Spirula are found only in the torrid zone. 



The food of the Mollusca consists of almost all sorts of sub- 

 stances, animal and vegetable, in all states, living or dead, fresh 

 or putrid ; but each species is in general confined to a certain 

 kind. 



The uses of the Mollusca in the economy of nature are va- 

 ried and extensive. They afford food to numerous animals, 

 especially fishes and birds, and to man himself. The savage 

 tribes which live along the coasts in many parts of the world 

 employ them much as an article of food. Even in civilized coun- 

 tries the Mollusca frequently form a considerable portion of 

 sustenance, although in general they are neither very pleasant 

 nor wholesome. The Cuttlefish furnishes a fluid from which 

 the pigment called China ink is procured ; and the ancients ex- 

 tracted the beautiful purple colour with which the garments of 

 their princes and nobles were dyed, from certain species of Pur- 

 puree inhabiting the coast of Tyre 



