NKW UNIONIDTI': OF THE UNITED STATES. 83 



Hah. — Near Coopa Eivcr, xYlabama. E. R. Sliowalter, M. D. 

 My cabinet, and cabinets of Dr. Showalter, Dr. Plartman and Mr. Antliony. 

 Diam. -7, Length -9, Breadth 1-2 inch. 



Shell smooth, ol)liqne. very much inflated, very inequilateral, obtu.sely angular be- 

 hind and obliquely rounded before; substance of the shell thick, thicker before; beaks 

 elevated, swollen ; ligament very short, rather thick and light brown ; epidermis light 

 brown, with a series of spots before the umbonial slope from the beaks to the maro-in, 

 with three or four regular, well marked, nearly equidistant marks of growth ; umbo- 

 nial slope raised and rounded ; posterior slope wide, subcordate, with an obscure im- 

 pressed line in each valve; cardinal teeth thick, pyramidal and crenulate; lateral 

 teeth thick, straight and short ; anterior cicatrices distinct, small and well impressed ; 

 posterior cicatrices distinct and well impressed ; dorsal cicatrices placed above the 

 centre of the cavity of the beaks; cavity of the shell small, rather deep and rounded; 

 cavity of the beaks somewhat deep and obtu.sely angular ; nacre silver white and 

 iridescent. 



Soft parts.— Branchial uterus not charged, but six specimens had ova in the ovarium. 

 Branchioi large, semicircular, very thin, inner ones much the larger, free nearly the 

 whole length of abdominal sack. Palpi very small, thin and suboval, united only at 

 the upper portion of the posterior edges. Mantle very thin, slightly thickened at the 

 edges. Branchial opening rather small, with numerous small brownish papilla). Anal 

 opening rather large, with very minute dark brown papilla) on the inner edges. Sriper- 

 anal opening small, edged with dark brown and .slightly united below ; color of the 

 mass dirty white. 



Eemarks.— This species is very nearly allied in outline, size and color to modicellus 

 (nobis). They are both very diminutive species, but robust. They may be distin- 

 guished at once by the colored spots on meclius, modicellus having in the same place a 

 few capillary rays, and it is not quite so much rounded as medius. Medim may be con- 

 founded with nucleopsis, Con., and at first I thought it was the young of that species 

 but having nine specimens before me, some of them evidently adult, I have no doubt 

 of their being different. Medius is a much smaller species, is more oblique, and has 

 more, larger and better defined spots in a row, which, in some specimen.s, are .'^o much 

 elongate as almost to constitute a ray from the beak to the margin. In some the 

 spots are not well defined. It is to be regretted that none of the females, six in num- 

 ber, had the ova in the branchial uterus. They were not of course developed, and 

 therefore the emhryonnc form could not be ascertained. They were sent to me in June, 

 in alcohol, by Dr. Showalter, and at that season incubation had not sufficiently ad- 

 vanced. None of the beaks wore perfect enough to show undulations. 



