OF THE UNITED STATES. 53 



Grypkuea, Sowerby. 



1. G. convexa, (Say.) PL iv, fig. 1, 2. 



Journ. Acad. Nat. Sciences, vol. vi, pi. iv. fig. 1, 2, and pi. v, 

 fig. 1, 2, 3. 



Syn. Ostrea convexa, (Say.) 



American Journal of Science, vol. ii, p. 42. 



Specific character. Oblong oval, smooth : upper valve thin, 

 very concave, concentrically striated; margin reflected ab- 

 ruptly upwards to meet that of its fellow : lower valve remark- 

 ably convex, smooth, biangulated from the hinge margin, with 

 a longitudinal indented line on one side ; a transversely wrin- 

 kled groove within on each side of the hinge ; cicatrix oval ; 

 beak broad, plane, remarkably incurved ; umbo not prominent. 



Length, two inches and three quarters ; breadth, two inches 

 and a quarter; depth, an inch and a quarter. 



Far. A. Umbo thick and prominent. Journ. Acad. vol. vi. 

 pi. v, fig. 1, 2 and 3. 



Far. B. Elongated. 



Abundant in the arenaceous marls of New Jersey, De- 

 laware and Alabama. 



2. G. mutabilis, (S. G. M.) pi. iv, fig. 3. 



Journ. Acad. Nat. Sciences, vol. vi, pi. iv, fig. 3. 



Specific character. Suborbicular, smooth, broadly expanded 

 each side of the beak ; both valves obliquely corrugated each 

 side of the hinge : upper valve slightly concave, concentrically 

 striated, outer edge reflected obliquely upwards to the disc of 

 its fellow, with a few lines radiating from the apex to the peri- 

 phery : lower valve convex, transversely undulated, lobed by a 

 longitudinal groove ; cicatrix subovate ; umbo prominent ; beak 

 slightly incurved. 



Length, four inches ; breadth, four inches and a half. 



