FRESH WATER AND LAND SHELLS. 285 



Anodonta denigrata. PI. XXV. Fig. 45. 



Testa hem, ellipticd, convexiuscula, inmquilaterali, untie? rotundatd; valvulis tenuibus; nalibus prominu- 

 iis, ad apices uiuliihttis ; epidermide polita, bruneo-nigricente, obsolete radiatd ; margaritd cseruled alba et 

 iridescente. 



Shell smooth, elliptical, somewhat inflated, inequilateral, rounded before; valves thin, beaks slightly prominent, 

 undulated at the tip; epidermis polished, blackish-brown, obscurely rayed; nacre bluish-white and iridescent. 



Hab. Campbell county, East Tennessee, President Estabrook. 

 My cabinet and cabinet of President Estabrook. 

 Diam. .8, Length 1.2, Breadth 2.2 inches. 



Shell smooth, elliptical, somewhat inflated, inequilateral, rounded before and very 

 slightly flattened on the anterior part, with a slightly curved dorsal line a little irregular 

 near the point of the beak; substance of the shell thin, very slightly thicker and whiter 

 before; beaks very small and very slightly prominent, rather concentrically undulate at 

 the tip; ligament thin and rather long; epidermis polished, blackish-brown, sometimes 

 dark-greenish-brown, and obtusely rayed, with distant marks of growth. Posterior slope 

 rather wide, and not much compressed ; with three rather obscure dark-green rays, from 

 the beak to the posterior margin; umbonial slope rounded and but slightly raised; anterior 

 cicatrices confluent; posterior cicatrices confluent; dorsal cicatrices immediately above 

 the centre of the cavity of the beaks; cavity of the shell not very deep, oval; cavity of 

 the beaks very shallow and rounded; nacre bluish-white and iridescent. 



Remarks. — This is rather a small species, of which President Estabrook sent me some 

 dozen specimens. It is a distinct species, and more nearly allied to An. Ferussaciana, 

 (Nobis,) than to any other species. It differs in being a smaller species, in bcino- more 

 compressed, and in having a much less callus on the dorsal margin. Indeed, in some of 

 the specimens no callus can be perceived. The undulations of the beaks are simple and 

 nearly concentric, like the Ferussaciana, but they are smaller. In all the specimens but a 

 half-grown one, there is a rough, opakc, white, carious mark of disease about the anterior 

 cicatrix and the cavity of the beaks. The younger one is without this mark of disease. 

 This specimen is greenish, and has the lines of growth very distinctly marked. 



Anodonta opaca. PI. XXV. Fig. 4G. 



Tenia hut, ellipticd, subinjlala, ineequilaterali, postice angulatd ; valvulis tenuibus; natibus tubpromi- 

 nentibus, ad apices undulatis ; epidermide opacd, nigricenlc, obsolete radiatd; margaritd alba ct iridescente. 



Shell smooth, elliptical, rather inflated, inequilateral, angular behind; valves thin, beaks rather prominent, 

 undulate at the tip; epidermis dark, almost black, obscurely rayed ; nacre white and iridescent. 



J lab. Near New Orleans, Mons. Janin. Eittle Rock, Arkansas, Prof. Powell. 

 My cabinet and cabinets of Prof. Powell and Dr. Hale. 

 Diam. 1.5, Length 2.1, Breadth 3.4 inches. 



Shell smooth, elliptical, rather inflated, inequilateral, angular behind, slightly curved on 

 the dorsal line; substance of the shell thin; beaks rather prominent and undulated at the 

 tip; ligament rather short and somewhat thick; epidermis dark, almost black, coarsely 

 . \. — 53 



