70 NEW UNIONID.E OF THE UNITED STATES. 



pallido moIle:1, cridiata, infernc striata; dentibus cardinalibus crassiusculis, compressis, erectis 

 striatisque ; lateralibus crassis, curtis, obliquis, rectis corrugatisque; niargarita alba et iridescente. 



Shell smooth, triangular, very much swollen, very inequilatei'al, subbiangular 

 behind, rounded before ; valves very thick, thicker before ; beaks very prominent, 

 swollen, very solid, incurved ; epidermis pale honey yellow, without rays, striate 

 below ; cardinal teeth rather thick, compressed, erect and striate ; lateral teeth thick, 

 short, oblique, straight and corrugate ; nacre white and iridescent. 

 Froc. Acad. Nat. Sci. 1861, p. 59. 



Hah. — Coosa River, Alabama. E. R. Showalter, M. D. 



My cabinet and cabinet of Dr. Showalter. 

 Diam. l-l, Length 1-2, Breadth 1-7 inch. 



Shell smooth, triangular, very much swollen, very inequilateral, subtriangular 

 behind, rounded before ; substance of the shell very thick, thicker before ; beaks very 

 prominent, tumid, very solid and incurved ; ligament short, thick and light brown ; 

 epidermis pale honey yellow, without rays, striate below, with rather close marks 

 of growth ; umbonial slope raised and rounded ; posterior slope cordate, wide, nearly 

 flattened, with an indistinct groove from the beaks to the margin ; cai-dinal teeth 

 rather thick, compressed, erect and striate; lateral teeth thick, short, oblique, 

 straight and corrugate; anterior cicatrices distinct, rather small and deeply im- 

 pressed; posterior cicatrices distinct, rather large and well impressed; dorsal 

 cicatrices situated above the centre of the cavity of the beaks ; cavity of the shell 

 rather deep and rounded ; cavity of the beaks shallow and angular ; nacre white and 

 iridescent. 



EemarJcs. — Two specimens of this massive little species are before me. The larger 

 is 1'7 inches wide, and the smaller r4 wide. It is near in outline to instructus herein 

 described, and to favideiis, Benson ; but while it is tumid on the umbones like the latter 

 species, it is very different in other characters, particularly in the color of epidermis, in 

 the teeth and in the nacre. It is much more inflated than insiructm, more solid, has 

 higher and more massive beaks, and evidently has not the large undulations of the 

 beaks of that species, although the tips are too much eroded to make them out. The 

 lateral teeth are remarkably massive, thickened at the end, and disposed to duplica- 

 tion in the right valve, as it is in the left one. In the full grown specimen, the upper 

 branch of the lateral tooth of the left valve is much smaller than that of the lower 

 branch, which is very thick and rugose. There is no appearance of a ray on either 

 of the specimens, but the younger one has an obscure spot on the umbonial sloj^e at 

 the intersection of the first line of growth. It is so solid a little species, that, together 

 with its color, one is reminded of a worn quartz pebble. 



