BIVALVES. MYA. 27 



ORDER If. 



l^tl)alb^0« 



MYA. — Truncate Trough-shell or Gaper. 



Animal — an Ascidia: Shell bivalve, generally gaping nt 

 one end; hinge with hroad, thicks strong teeth, seldom 

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



THIS genus has been placed by LinnsEUs the first on the 

 list of Bivalves: its species are by no means numerous, 

 twenty-seven only having been described by him. 



The principal characteristic of the My a consists in its 

 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 difFerenly shap- 

 ed; for, in the Pholas, it is long and slender, and almost 

 of equal size throughout ; whereas, in the Mya it is much 

 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 some are entirely without 



