CHIEFLY OF THE UNITED STATES. 41 



angular behind, truncate before; valves thick, thicker before; beaks prominent, 

 swollen, incurved, rugosely undulate at the tips ; ej^idermis honey yellow, shining, 

 covered with interrupted rays ; cardinal teeth rather small, subconical and corru- 

 gate; lateral teeth short, oblique and straight; nacre silver white and very 

 iridescent. 



Proc. Acad. Nat. Sci., 1861, p. 392. 



Hah. — Nolachucky River, Tenn., J. G. Anthony. 



My cabinet and cabinet of Mr. Anthony. 

 Diam. -7, Length -8, Breadth 1-1 inches. 



Shell smooth, quadrate, cubical, very much swollen, very inequilateral, obtusely 

 angular behind and truncate before ; substance of the shell thick, thicker before ; 

 beaks prominent, swollen and incurved ; ligament very short ; epidermis honey 

 yellow, shining, with interrupted green rays on the sides and with rather close lines 

 of growth ; umbonial slope very much raised and obtusely angular : posterior slope 

 cordate, flattened, with a few obscure rays ; cardinal teeth rather small, subconical 

 and rough ; lateral teeth short, oblique and straight ; anterior cicatrices distinct, 

 rather large and very deeply impressed ; posterior cicatrices distinct, moderately 

 large and well impressed ; dorsal cicatrices placed immediately over the centre of 

 the cavity of the beaks ; cavity of the shell rather deep ; cavity of the beaks shallow 

 and obtusely angular ; nacre silver white and very iridescent. 



Remarlcs. — A single specimen only of this unusually shaped little species was sent 

 to me by Mr. Anthony. It is an inch and two-tenths wide, by eight-tenths long, 

 and the diameter being seven-tenths, it closely approaches a cubical form. It may 

 not be full grown, but I suspect that it does not obtain a much larger size, there 

 being nine lines of growth upon it. The interrupted rays rise at the lines of 

 growth and fade before reaching the next lower one. This specimen has these rays 

 on the sides only, the anterior part having none, while the posterior slope has two or 

 three very indistinct ones. Others no doubt will be found well covered with rays, 

 and others again with still fewer. The nacre of the posterior portion is thin enough 

 to permit the rays to show through it, while the anterior and upper portions are 

 thick and dense. The beaks are not perfect, but the undulations remaining show 

 that they are few and rather coarse. In outline this species is nearest to arcceformis, 

 (nobis,) but it differs in many respects, and cannot be confounded with that interest- 

 ing species. It is a much smaller shell, has not the elevated umbonial slope, nor the 

 groove or carina of the posterior slope. In the system of rays they totally difler, the 

 arca'formls having capillary rays over the whole disk, while this has interrupted rays 

 on the sides, which are flattened. The anterior end is also more enlarged and 

 flattened. I think from the form this is a male. 



11 



