NEW UNION ID.li OF THE UNITED STATES. 01 



small, dei^ressed and striate; lateral teeth rather short, very thick, obli([ue, corrugate 

 and straight; nacre silver white and iridescent. 

 Proc. Acad. Nat. Sci. 18G1, p. .^9. 



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



My cabinet and cabinet of Dr. Showalter. 

 Diam. -9, Length 1-3, IJrcadth 1^ inches. 



Shell smooth, triangular, swollen at the umbones, ine([uihiteral, angular Ijchind, ob- 

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

 prominent and swollen ; ligament rather short, somewhat thick and greenish brown ; 

 epidermis brownish green, obscurely rayed, and transversely and closely striate, with in- 

 distinct, distant lines of growth; umbonial slope much raised and acutely angular; 

 posterior slope elliptical, flattened, yellowish, with a few obscure capillary lines, with 

 two obscure, impressed lines from the tips to the posterior margin ; cardinal teeth 

 rather small, depressed and striate ; lateral teeth rather short, very thick, oblique, 

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

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

 placed above the centre of the cavity of the beaks; cavity of the shell rather deep, 

 irregular, and deeply and obliquely guttered in the middle ; cavity of the beaks rather 

 shallow and rounded. 



Remarls. — A single specimen only of this interesting species was received from 

 Dr. Showalter. In outline it is very nearly the same as Woodward ianus (nobij*), but 

 differs in the color of the epidermis, in the rays, which are closer and not interrupted, 

 and in the greater thickness of trinacrus. The lateral teeth are much thicker and 

 more blunt at the posterior termination. It is about the same size, but still may 

 easily be distinguished. The beaks are too much eroded to observe any undulations. 

 The specimen before me seems to be adult, and well developed. The disk, up to 

 the angular edge of the umbonial slope, is dark olive green, the color being caused by 

 the close, broad, greenish rays, showing obscure, yellowish intervals. The yellow face 

 of the posterior slope comes up sharply to this angle of the umbonial slope. The 

 irregular, waving surAice of the interior is very remarkable, having a deep gutter in 

 the centre from the beaks to the posterior basal margin. It is greatly to be regretted 

 that we have not the soft parts of the female in a state of development to exhibit 

 the brancJiial uterus, which, I suspect, will prove to be much like that of Wood- 

 toardianufi, as well, also, the embryonic form. 



Unio decumhens. pi. 12, fig. 236. 



Testa hevi, arcuata, vald6 cotnpressa, ad latere planulata, insequilaterali, postic^ biangulata, autico rotun- 

 da ; valvulis 8ubtenuibu8, antice et postici- paulisper crassioribus ; natibus promiDulis ; epidcrmidc 



