NEW FRESH AVATER AND LAND SHELLS. 197 



fluent; dorsal cicatrix placed in the centre of the cavity of the beaks; cavity of 

 the shell rather deep and rounded; cavity of the beaks very shallow; nacre 

 white and very iridescent at the posterior margin. 



Remarks. — A single specimen only of this shell came in the collection from 

 Mr. Edgar. It has no remarkable characteristics, yet it cannot be referred to any 

 species known to me. It has some resemblance to U. pictormn, Lam., and is 

 somewhat like U. lanceolatus (nobis,) but may be easily distinguished from both 

 these species. I presume it is always without rays, — the individual before 

 me having no trace of them. 



Unio biangulatus. Plate 9, Fig. 8. 



Testa obovatd, inflatd, postice biangulari; valvulis tenuibus; natibus subprominentibus ; epidermide 

 tenebroso-fuscd; radiatd; dentibus cardinalibus subgrandibus, elevatis; lateralibus subgrandibus curvis- 

 que; margaritd alba et iridescente. 



Shell obovate, inflated, bjangular behind; valves thin; beaks rather prominent; epidermis dark brown, 

 rayed ; cardinal teeth rather large, elevated ; lateral teeth rather large and curved ; nacre white and iridescent. 



Hab. Cany Fork River, Tenn. Prof. Troost and Mr. S. M. Edgar. 

 My Cabinet, and Cabinets of R. O. Currey, M. D., Mr. Edgar and Prof. Troost. 

 Diam. 1.2, Length 1.8, Breadth 2.8 inches. 



Shell obovate, inflated, biangular behind; substance of the shell thin, thicker 

 before; beaks rather prominent, approximating the anterior margin; ligament 

 rather long and thick; epidermis dark brown, sometimes yellowish, with in- 

 distinct interrupted rays on the posterior portion; umbonial slope subangular; 

 posterior slope with an imperfect fold which makes a second angle; cardinal 

 teeth rather large, erect, pointed, double in the left valve and single in the 

 right; lateral teeth rather large and curved, lamellar near the termination; an- 

 terior cicatrices distinct; posterior cicatrices confluent; dorsal cicatrices large 

 and placed on the upper side of the cavity of the beaks; cavity of the shell 

 large; cavity of the beaks rather deep and angular; nacre white and iridescent. 



Remarks. — When the specimen is entirely perfect, the double angle of the 

 posterior margin marks this shell very distinctly. It has some resemblance to 



