MY A GAPER. 149 



The cavity. 



The disk, the convex part of the valves 

 between the umbones and margin. 



The lengthy the direction of the shell from the 

 beak to the base. 



The breadth, the direction at right angles with 

 the length. 



The auricula* or ears, small appendages placed 

 at the sides of the hinge. 



The circumference. 



The muscular impressions, marks in the inside 

 of the shell made by the adhesion of adductor 

 muscles. 



The right valve, the valve nearest to the right 

 hand, when the shell is placed on its base with 

 the area opposite to the person looking at it. 



The left valve. 



The teeth, pointed protuberances at the hinge. 



The cardinal teeth, the central teeth, or those 

 near the centre of the hinge. 



The lateral teeth, the teeth near the sides. 



Genus. MYA.f P/wroZ, Myce. 



GAPER. 



Generic Character. Shell bivalve, equivalve, 



* Auricula, a small ear ; the diminutive of the Latin 

 auris, an ear. 



f Plate VII. fig. 1, 2. 



