18 



CHAP. VI. 



BIVALVES. 

 MYA, or Trough Shell. 



Q. WHAT are the distinguishing character- 

 istics of the Mya, Trough-shell, or Gaper? 



A. Shell bivalve, mostly gaping at both ends : 

 hinge seldom with more than one tooth, solid, 

 thick, and spreading, proceeding from beneath 

 the beak. 



Q. Describe the form of the shells. 



A. They are chiefly broader than they are 

 long, and generally smooth, or slightly striated, 

 (varied with channels). The hinge, in some spe- 

 cies, is connected internally by an elastic carti- 

 lage, which in one valve is sunk in a triangular 

 sinus or hole ; and in the other is protected by a 

 broad tooth. In others the cartilage is wanting, 

 and the tooth varies in appearance,- sometimes 

 two-lobed, with one of the lobes slightly inserted. 

 This genus is rather to be distinguished by llie 



