GASTEROPODA. 



153 



or internal appendage, and with the margin undivided, 

 though sometimes marked or waved by the external ribs, 

 or striae ; apex inclined towards the front part of the shell, 

 where the head of the animal 

 is situated, the mark of which 

 can generally be traced in 

 the interior by the muscular 

 impression being there inter- 

 rupted. Animal, head very 

 distinct and supporting two 

 tentacula, having eyes at the 

 outer and lower extremity ; branchiae placed between the 

 mantle and the foot, and nearly reaching round the body ; 

 foot a large disk; head with cartilaginous jaws, and a 

 very long tongue, armed with transverse rows of teeth. — 

 About 100 species; also fossil. 



The genus Patella is to be found in all parts of the 

 world, chiefly on rocky coasts, and often where the sea 

 breaks with considerable violence; many species, (from 

 the shape of the shell corresponding exactly with that of 

 the rock on which they have lived,) appear never to move 

 from the spot they have once selected, and even form in 

 most cases cavities in the rock itself, by a power they pos- 

 sess of absorbing its substance : the Patella vulgata of the 

 British coast has this property. 



The Patella cochlea is found at the Cape of Good Hope ; 

 it lives almost exclusively attached to a larger species of 

 the same genus, on the surface of which it forms a flat 

 disk exactly the size of its mouth. To form these flat 

 disks (of which there are so generally two, one on each 

 side of the apex of the larger Patella, as almost to form a 

 character of the species), and to assist in the increase of 

 its size, the animal appears to absorb the coralline, or other 



