OSTHEA, 



GENERIC CHARACTER. 



Shell bivalve, attached, fuliaceous. inacquivalve, irregu- 

 lar; apices becoming very unequal by a^e, the position of 

 the superior valve being gradually changed with respect 

 to the lower valve produces a corresponding elongation of 

 the inferior apex : superior valve depressed ; inferior valve 

 larger, concave ; liinge without teeth, tripartite, the mid- 

 dle portion in the inferior valve being a longitudinal groove 

 for the reception of the cartilage, corresponding with a 

 convexity of the upper valve ; ligament attached to the la- 

 teral portions ; muscular im])ression cue. large, subcen- 

 tral. 



Animal depressed, margins of the mantle thick, not ad- 

 lierent, retractile, with a double range of short and numer- 

 ous tentacular filaments ; labial palpi long triangular ; foot 

 none ; muscle bipartite, subccntral, no prominent syphon 

 and no byssus. 



OBSERVATIONS. 



Oysters arc familiar to the knowledge of all those who 

 reside in maratime districts, in almost every part of the 

 globe. Under a rugged and irregular exterior is included 

 an animal which supplies the most delicate food. and which 

 has accordingly been eagerly sought for in all ages, as one 

 of the chief luxuries of the table. Although the consump- 



ri. 53. 



