FRESH WATER AND LAND SHELLS. 27 



sidcred the type. In its outline it approaches the luleohis, Lam., but is not quite so trans- 

 verse, while it is more so than cariosus. Two of the specimens are richly salmon-coloured 

 in the cavity of the shell — the others are all white. The females are very much enlarged 

 over the umbonial slope, and expanded at the posterior basal margin. None of the speci- 

 mens which I received have any rays. 



I have named this species in honour of Prof. W. Byrd Powell, of Memphis, Tcnn. 



Unio affinis. pi. XIX. Fig. 26. 



Testa Isevi, eUiptica, convcxu, inequilaterali, postice rotundata ; vidvulis subtenuibiis; natibus suhpromi- 

 nentibus; epidermide radiatd, luteola, nitidd; dentibus cardinalibus parvis, compres.iis, obliquis, acurninalis, 

 crenuhilis ; laleralibus sublongis, lameUatis subcurvisque ; margarila alba et iridescenlc. 



Shell smooth, elliptical, convex, inequilateral, rounded behind; valves rather thin; beaks rather prominent, 

 epidermis rayed, yellowish, shining; cardinal teeth small, compressed, oblique, acuminate, crenulale; lateral 

 teeth rather long, lamellar and rather curved; nacre white and iridescent. 



Hab. Alexandria, Louisiana, J. Hale, M. D. 



My cabinet. 

 Diam. .9, Length L4, Breadth 2.1 inches. 



Shell smooth, elliptical, convex, inequilateral, rounded behind and inflated over the 

 umbones; substance of the shell rather thin; beaks rather prominent, placed towards the 

 anterior margin; ligament rather short and somewhat thick; epidermis shinrng, yellowish, 

 with numerous rays and rather distant marks of growth; posterior slope rather elevated; 

 umbonial slope rounded and inflated; cardinal teeth small, compressed, oblique, acuminate, 

 crenulate, double in both valves; lateral teeth rather long, lamellar, slightly curved, 

 separated from the cardinal tooth; anterior cicatrices distinct; posterior cicatrices con- 

 fluent; dorsal cicatrices placed across the cavity of the beak under the cardinal tooth; 

 cavity of the shell rather deep and rounded; cavity of the beaks rather shallow and sub- 

 angular; nacre white and iridescent. 



Remarks. — The outline of the specimen before me is of a remarkably regular oval. It 

 belongs to the group of which cariosus. Say, may be considered the type. It is nearest in 

 general character to U. crocalus, (Nobis,) but it is a larger species, not angular behind, 

 and the rays are broader. 



Unio proximus. PI. XX. Fig. 27. 



Tesid Ixvi, el/ipficd, subinjfafd, siibinxqidJuterali, posliee rohindiitd: valvu/is lennibiis ; nalilnm parvi.s, 

 sitbprominentibus ; epidermide luted, radiatd; dentibus cardinalibus valde compressis, obliquis, acurninalis; 

 lateralibus longis, lamellalis subreclisque; margaritd alba et iridescente. 



Shell smooth, elliptical, somewhat inflated, subinequilateral, rounded behind; valves thin; beaks small, some- 

 what prominent; ejiidermis yellowish, radiated; cardinal teeth much compressed, oblique, acuminate; lateral 

 teeth long, lamellar and nearly straight; nacre white and iridescent. 



Hab. Georgia. J. P. Barratt, M. D. 



My cabinet and cabinet of Dr. Barratt. 

 Diam. .7, Length 1.2, Breadth 2.1 inches. 



