anterior extremity, the posterior basal emargination 

 much less profound, and the central tubercles are 

 obsolete: in outline it closely resembles U. obliqiiatus, 

 but that species is always of a purple colour within, 

 though the tint is sometimes pale. 



Inhabits the "Wabash river, Indiana, and Detroit 

 river, Michigan. 



UXIO TERES. 



Plate XXVIII. 

 DESCRIPTION. 



Shell narrow — elliptical, subcylindrical. moderately 

 thick; umbo slightly prominent; summit obtusely 

 rounded; umbonial slope abruptly rounded, submar- 

 ginal; posterior side produced, cuneiform: epidermis 

 yellowish and polished, rarely rayed; within white or 

 pale salmon colour; cardinal teeth double in each 

 valve, subcompressed. vers* erect; lateral teeth distant 

 from the cardinal teeth. 



SYNONYMES. 



U. teres, Raf. Ann. gen. des Sc. Phys. vol. v. p. 55. Poulson's 



trans, p. 68. 

 U. anodoxtct.des, Lea. Trans. Amer. Philos. Soc, new series, 



vol. iv. p. 91, pi. viii. fig. 11. 

 Cab. A. V. S. No. 1385. 



OBSERVATIONS. 



A well characterized species, approaching the rec- 

 tus in outline, but is comparatively shorter and emi- 



