82 NEW UNIONID.E OF THE UNITED STATES. 



lateral teeth short, thick, corrugate, oblique and nearly straight ; nacre white and 

 iridescent. 



Proc. Acad. Nat. Sei. 18G1, p. 59. 

 Hab. — Cahawba River, Alabama, E. R. Showalter, M. D. 

 My cabinet and cabinet of Dr. Showalter. 

 Diam. ll, Length 1-5, Breadth 2 inches. 



Shell smooth, subtriangular, inflated, inequilateral, subbiangular behind, rounded 

 before; substance of the shell thick, thicker before; beaks a little prominent and 

 thick ; ligament large and dark brown ; epidermis reddish-brown, rather rough, with- 

 out rays and with somewhat close lines of growth ; umbonial slope raised and ob- 

 tusely angular; posterior slope narrow cordate, slightly carinate, with two impressed 

 lines on each valve from the beaks to the posterior margin ; cardinal teeth very large, 

 deeply and numerously sulcate, erect, compressed and crenulate ; lateral teeth short, 

 thick, corrugate, oblique and nearly straight; anterior cicatrices distinct, rather small 

 and very deeply impressed ; posterior cicatrices confluent, moderately large and well 

 impressed ; dorsal cicatrices placed along the side and base of the cardinal teeth ; 

 cavity of the shell rather shallow and wide ; cavity of the beaks deep and angular; 

 nacre white and iridescent. 



Remarks. — Among the interesting specimens sent to me by Dr. Showalter were two 

 ' which though somewhat different are, I think, of the same species. The smaller 

 one is only half grown, and may not j)rove when we get suites really to be the same, 

 as I observe some well marked difference. The older one is evidently mature, and 

 being somewhat eroded, may not be perfect in the characters above described. It 

 belongs to the triangular group of species approaching to obliqueness. The umbones 

 ar-e high, and the disks somewhat inflated. It is near to instrndus, herein described 

 in outline, but it has a rougher epidermis, and is more inflated. The beaks of neither of 

 the specimens are perfect enough to show any undulations. The older one has some 

 rough furrows along some of the marks of growth. 



UniO MEDIUS. PI. 10, fig. 227. 



Testa Isevi, obliqua, valde inflatfi, valde insequilaterali, postice obtuse angulatii, antico oblique rotundata; 

 valvulis erassis, postic^ crassioribus ; natibus elevatis, tutnidis; epiderniide fusca, maculata, inferoe 

 striata, superne micanti ; dentibus cardinalibus crassis, pyramidatis crenulatisquej^lateralibus crassis, 

 rectis brevibusque; margarita argentea et iridescente. 



Shell smooth, oblique, very much inflated, very inequilateral, obtusely angular 



behind, obliquely rounded before ; valves thick, thicker before ; beaks raised, swollen ; 



epidermis brown, spotted, striate, shining below ; cardinal teeth thick, pyramidal and 



crenulate ; latei-al teeth thick, straight and short ; nacre silver white and iridescent. 



Proc. Acad. Nat. Sci. 1861, p. 40. 



