318 



POPULAR CONCHOLOGY. 



equal, that of the lower valve becoming very large with 

 age and attached, upper valve flattened and smaller ; no 

 teeth, ligament nearly internal, 

 lodged in a pit. Animal shaped 

 like the shell, its mantle freely 

 open, and without tubes, the 

 edges double, and each bordered 

 by short tentacular fringes ; no f 

 conspicuous ocelli ; branchial leaf- 

 lets not doubled on themselves ; 

 labial appendages triangular, con- 

 nected round the mouth by a 

 plain membrane ; foot obsolete.* 

 — Many species: also fossil. 



Oysters have been found in 

 most parts of the world in abun- 

 dance, although none have as yet been discovered in the 

 polar regions : they are inhabitants of salt water only, 

 and are always found on rocky ground, at no great depth 

 from the shore, attached by the under valve. The oyster, 

 and indeed all bivalves which adhere by the shell, are 

 covered at their birth with a mucilaginous liquid which 

 attaches them to the surface of any object on which they 

 rest. The animal strengthens this first adhesion in the 

 same manner that it increases the size of its shell. At 

 the mouths of several American, African, and Indian 

 rivers, great quantities of oysters are found attached to 

 the roots of trees, and even to their branches, where they 

 are so situated as to be covered by the tide. Mrs. Lee, 

 in her " Stories of Strange Lands," says, " The flavour of 

 the tree-oyster is delicious ; they are small, and cover the 

 lower branches of the mangroves. Two or three of these 



Ostrea eduliv. 



* Forbes' s British Moll. 



