-244 DESCRIPTION OF 



Shell regularly elliptical, somewhat inflated, inequilateral, rounded on the 

 umbonial slope; substance of the shell rather thin, thicker before; beaks 

 scarcely prominent; epidermis yellowish brown with rather regular raj^s over 

 the whole disk; cardinal teeth very small, single in the right and double and 

 deeply cleft in the left valve ; lateral teeth long and curved along the dorsal 

 margin; anterior cicatrices distinct; posterior cicatrices confluent; dorsal 

 cicatrices placed within the cavity on the under side of the cardinal teeth; 

 cavity of the shell rather deep and rounded, cavity of the beaks very shallow 

 and slightly angular ; nacre bluish and iridescent. 



Remarks. — In its regular elliptical form this shell resembles U. radiatus. It 

 also resembles U. pictus, nobis, in some degree, but is more inflated and a much 

 darker-coloured shell. The teeth are remarkably small, and in the three spe- 

 cimens before me disposed to be carious. 



Unio m^stus. Plate 26, Fig. 60. 



Testa ellvptica, subinflatd, valdk incEquilaterali; valvulis subcrassis; natibus prominulis; epidermide 

 tenebroso-fuscd, rugoso-striatd; dentibus cardinalibus parvis, lateralibus longis curvisque; margaritd 

 atro-purpured et iridescente. 



Shell elliptical, somewhat inflated, very inequilateral; valves somewhat tliick; beaks somewhat promi- 

 nent; epidermis dark brown, roughly striate; cardinal teeth small ; lateral teeth long and curved; nacre 

 dark purple and iridescent. 



Hab. French Broad River, East Tenn. Dr. Troost and S. M. Edgar. 

 My Cabinet, and Cabinets of Dr. Troost and Mr. Edgar. 

 Diam. .8, Length 1.1, Breadth 2 inches. 



Shell elliptical, inflated, rounded on the umbonial slope, equally rounded 

 before and behind, very inequilateral; substance of the shell somewhat thick, 

 thinner behind; beaks somewhat prominent, placed near to the anterior mar- 

 gin; ligament rather short and thin; epidermis dark brown, nearly black and 

 roughly striate; cardinal teeth small, single in the right and double and deeply 

 cleft in the left valve ; lateral teeth long, thin and somewhat curved ; anterior 

 cicatrices distinct; posterior cicatrices confluent; dorsal cicatrices placed across 

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

 the beaks very small ; nacre dark purple and iridescent. 



