85 



species from Harpeth river, Tennessee. It cannot 

 be confounded with U. stegarius, in consequence of 

 its remarkable gibbose disk. The rays are more 

 strongly marked than those of the latter species; the 

 disk is never tuberculated, whilst the stegarius is 

 sometimes covered with tubercles, as Mr. Lea has 

 stated in his remarks upon the dromas. A single 

 valve in my cabinet measures about four inches from 

 beak to base. 



UNIO SUBTENTUS. 



Plate XL VII. —Fig. 1. 



DESCRIPTION. 



Shell oblong-suboval, very widely and slightly con- 

 tracted at base; summits hardly elevated, decorti- 

 cated, obtusely rounded; posterior basal angle a little 

 prominent, rounded; posterior dorsal slope with nu- 

 merous subramose, slightly arcuate, oblique, parallel 

 costse; epidermis with broad interrupted green rays, 

 sometimes obsolete; within reddish-fulvous; cavity of 

 the umbo not deep; cardinal teeth somewhat direct, 

 not transverse; lateral teeth slightly arcuate. 



SYNONYME. 



U. subtentus, Say. Jour. Acad. Nat. Sc, vol. v. p. 130. 



Amer. Conch., pi. xv. 

 Cab. Ji. N. S„ JVo. 20417. 



OBSERVATIONS. 



Mr. Say observes, " in general outline, this shell 



