35 



ORDER II, 



BIVALVES. 



MYA. TRUNCATE TROUGH-SHELL OR GAPEK. 



Animal an Ascidia: Shell bivalve, generally gaping at 

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

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

 THIS genus has been placed by Linnaeus the first on 

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

 forty only having been described by him. 



The principal characteristic of the Mya 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 ; for, in the Pholas, it is long and slen- 

 der, 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 appearance 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 it ; 

 others, again, have two or three teeth, and, in some in- 

 stances, small crenulations supply the place of a regular 

 hinge. 



The form of the Mya varies exceedingly, some are ob- 



