NEW FRESH WATER AND LAND SHELLS. 237 



rounded; cavity of the beaks very small and subangular; nacre white and iri- 

 descent. 



Remarks. — In its outline this species resembles U.folliculatus, (nobis.) It 

 differs in being more cylindrical and in having a much smaller cardinal tooth. 

 The cardinal tooth is very remarkable for its small size, being little more than 

 two small tubercles on the dorsal line. The only specimen before me is white : 

 others may differ in colour. On the sides are a few obscure transverse folds. 

 The breadth and flatness of the posterior slope is very remarkable. 



Unio Bigbyensis. Plate 22, Fig. 51. 



Testa subtriangulari, compressd, incBquilaterali, postice angulatd; valvulis subcrassis; natibus pro- 

 minentibus ; epidermide luted, valde radiatd; dentibus cardinalibus magnis erectisque ; lateralibus mag- 

 nis suhrectisque; margaritd vel alba vel salmonis colore tincta. 



Shell sub-triangular, compressed, inequilateral, angular behind; substance of the shell rather thick ; beaks 

 somewhat prominent; epidermis yellow, very much rayed; cardinal teeth large and erect; lateral teeth 

 large and nearly straight; nacre white or salmon-coloured. 



Hab. Big Bigby Creek, Maury Co., Tenn. T. R. Button. 

 My Cabinet, and Cabinet of Mr. Button. 

 Diam. .8, Length 1.5, Breadth 2.1 inches. 



Shell sub-triangular, compressed, inequilateral, angular behind; substance 

 of the shell rather thick, thinner behind; beaks somewhat prominent, undu- 

 lated at the tip; ligament rather long and thick; epidermis yellow, with nume- 

 rous broad green rays; posterior slope somewhat carinate and free from rays; 

 cardinal teeth large and erect, disposed to be double in both valves; lateral 

 teeth large, thick and nearly straight; anterior cicatrices distinct; posterior 

 cicatrices distinct; dorsal cicatrices placed under the plate, posterior to the car- 

 dinal tooth; cavity of the shell very shallow; cavity of the beaks shallow and 

 angular ; nacre white or salmon-coloured. 



Remarks. — This species has a strong resemblance to U. ruhiginosus, (nobis,) 

 in its outline and in its nacre. They are both found occasionally white. When 

 I described ruhiginosus, I had not seen a specimen with a white nacre. The 

 Bigbyensis differs from it in having numerous broad rays, while those on the 



