196 DESCRIPTION OF 



Shell nearly round, somewhat inflated; valves thick; beaks prominent; epidermis brown, striate with 

 spotted rays; cardinal teeth rather large; lateral teeth small and straight; nacre white and iridescent. 



Hab. Cany Fork and Holston Rivers, Tenn. S. M. Edgar. 

 Mj Cabinet, and Cabinet of Mr. Edgar. 

 Diam. .7, Length 1.3, Breadth 1.5 inches. 



Shell nearly round, somewhat inflated; substance of the shell thick, thinner 

 behind; beaks prominent; ligament rather long and thin; epidermis brown, 

 striate, with several interrupted rays over the umbones; lines of growth ap- 

 proximate; cardinal teeth rather large, single in the right and double in the 

 left valve; lateral teeth small and straight; anterior cicatrices distinct; posterior 

 cicatrices distinct; dorsal cicatrices placed under the cardinal tooth; cavity of 

 the shell rather deep and rounded; cavity of the beaks deep and angular; nacre 

 white and iridescent. 



Remarks. — Two specimens only of this species were brought by Mr. Edgar. 

 It seems to be most nearly allied to U. suhrotundus (nobis;) but differs in the 

 rays, in being less polished, in being less inflated and particularly in having 

 the marks of growth more approximate, and more numerous. 



I name this shell after the distinguished naturalist and companion of Peron, 

 my old friend C. A. Lesueur. 



XJnio dactylus. Plate 9, Fig. 7. 



Testa transversa, subinflatd; valvulis tenuibus; natibtis prominulis ; epidermide luted; dentibus car- 

 dinalibus minimis, erectisque ; lateralibus longis subcurvisque ; margarita alba et iridescente. 



Shell transverse, rather inflated; valves thin; beaks somewhat prominent; epidermis yellow; cardinal 

 teeth very small and erect; lateral teeth long and rather curved; nacre w^hite and iridescent. 



Hab. Cany Fork River, Tenn. S. M. Edgar. 



My Cabinet, and Cabinet of Mr. Edgar. 

 Diam. .6, Length .1, Breadth 1.9 inches. 



Shell triangular, inflated, narrow-elliptical; substance of the shell thin, 

 thicker before; beaks somewhat prominent; ligament rather long and thin; 

 epidermis yellow; umbonial slope rounded; cardinal teeth very small, erect, 

 pointed in the left valve, the anterior lobe being much the highest; lateral 

 teeth long and rather curved; anterior cicatrix distinct; posterior cicatrix con- 



