24 BIVALVES. MVA. 



II. 



i3ibalbe0. 



MYA. — Truncate Trough-shell or Gaper. 



Animal — ariAscidia: Shell bivalve, (jeneralh/ ffapiuff at 

 one end; hinge with broad, thick, strong teeth, seldom 

 more than one, and not inserted into the opposite valve. 



THIS genus may properly be called the first on the list 

 of Bivalves; its species, however, are by no means nu- 

 merous, their number being limited to twenty-six. 



The principal characteristic of the My a consists in i(s 

 gaping at one end: the next general distinguishing mark 

 is, its having a single, broad, patulous tooth, proceeding 

 from beneath the beak. This tooth differs from that of 

 the foregoing genus, in as much as it is otherwise sliaped ; 

 for, in the pholas, it is long and slender, and almost of 

 equal size throughout; whereas, in the Mya, it is nnuh 

 wider and broader at one end than the other; and the 

 broadest end has an excavation, which gives it the ap- 

 pearance of the bowl of a spoon or ladle. 



However, this sort of tooth is not always discernible in 

 every species of the Mya, for sonic are entirely without 



