MOLLUSCA OR UNIVALVES. 145 



on the surface of which it forms a flat disk ex- 

 actly 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 ani- 

 mal appears to absorb the coralline, or other 

 similar substances, with which the larger shells 

 are abundantly covered.* 



There are other species, on the contrary, 

 which do not remain entirely attached to the 

 same place, but occasionally move ; and others, 

 again, which fix themselves to sea-weeds, which 

 appear to be the food of the whole genus. 

 They are particularly abundant at the Island of 

 Cyprus and the Cape of Good Hope ; where 

 they are often found of a very large size, and 

 i are used as spoons by the Hottentots. The 

 common English species is generally smooth on 

 the outside ; but many of the foreign ones are 

 covered with ridges in rays from the apex to 

 I the circumference. Sometimes these ridges 

 I . extend beyond the edge of the margin, and ap- 



* Gray, Philosophical Transactions, 1833. 

 L 



