114 



pression on the posterior side; middle of the valves 

 with an oblique slightly elevated tuberrulated ridge, 

 the tubercles becoming more numerous and promi- 

 nent with age; dorsal margin very oblique, straight; 

 posterior side somewhat produced, the end margin 

 obliquely truncated, extremity truncated obliquely 

 inwards; l>eaks prominent; epidermis brownish-yel- 

 low, polished, not rayed; surface with remarkably 

 deep distant lines of growth <>r furrows; basal mar- 

 gin projecting in the middle and emarginate poste- 

 riorly; within white; cardinal teeth double in one 

 valve, single in the opposite valve, deeply striated 

 and rough; lateral teeth rectilinear and very oblique; 

 anterior muscular impression profound; posterior 

 very slightly impressed. 



BTNONTMGfl 



I*. cvfhia, Raj. Ann jrcn. des Sc. Phya., roi. * |>- 39. Poul- 



son's trans., p. •'(;». 

 V. F.soM s, dretn. Contribution* of tba Maclurian Lyceum, vol. 



i. p. 4fl, pi. %. 



OMEftVATK !ffi 



This specie* is nearly allied to U. ricatricomu, Say, 

 but is very easily distinguished in young and middle 

 aged specimen! 1»\ the lighter coloured and more 

 polished epidermis. The specimen figured belongs to 

 the cabinet of C. V. Poulson, Esq., in which is also 

 the original specimen described by Rafinesque. 



Inhabits the Ohio and its tributaries. Dr. Green 

 observes that he obtained eight or ten of these shells 

 from the rivers in the neighbourhood of Pittsburgh. 



