CONCHIFEKA OR BIVALVES. 129 



a preserve, which is a kind of tank dug in the 

 sand near the sea, and communicating with it 

 by a narrow passage ; this place is frequently 

 cleared of mud and dirt by letting the water 

 run off and refilling it ; by this means the 

 quality of the oyster is much improved. They 

 are not considered wholesome during May, 

 June, July, and August, and are not eaten until 

 they are one year and a half old. 



The animal of the oyster appears to be one of 

 the most inanimate of the Mollusca ; it remains 

 fixed upon a rock, or other submarine object, 

 enjoying only the nourishment brought it by 

 the waves, and giving scarcely a sign of life, 

 except the opening and shutting of its valves. 



The genus Gryphcea of Lamarck is by Des- 

 hayes and other conchologists incorporated with 

 the genus Ostrea. 



83. Placuna. — Shell nearly equivalve, ir- 

 regular, very much 

 compressed, irides- 

 cent ; two internal 

 cardinal teeth in one \\ 

 valve, shaped like a \ 

 V., and in the other 



K 



