81 



posterior slope dilated, with nodules towards the 

 margin; beaks slightly elevated, granulate at tip; 

 epidermis olive-brown and rather smooth; within 

 white; cardinal teeth large and prominent; lateral 



teeth subrectilinear. 



i 



SYNONYMES. 



U. nodulata, Ruf. Ann. gen. des Sc. Phys., vol. v. p. 41, pi. 



lxxxi. figs. 17, 18. Poulson's translation, p. 42. Say. Ainer. 



Conch., No. 6. Ferrus. Mag. de Zool. 

 U. pustulatus, Lea. Trans. Amer. Phil. Soc, new series, vol. 



iv. p. 79, pi. vii. fig. 9. 

 Cab. A. N. S., No. 1755. 



OBSERVATIONS. 



Inhabits the Ohio river and its tributaries. It is 

 related to U. bullatus and U. Mortoni. From the for- 

 mer it differs in the regularity of its tubercles, in the 

 dilatation of the posterior slope, and in the absence 

 of the broad green ray on the umbo. From the latter 

 it may be distinguished by the same characters, and, 

 in addition, by the want of a broad depression or 

 furrow, which characterizes U. Mortoni. Rafinesque's 

 outlines of this shell, though rude, are characteristic 

 enough; and his description, though short, perfectly 

 clear and applicable to this species only. 



