epidermis pearly white : surface rough and scaly, wrink- 

 led transversely and waved longitudinally, having distinct 

 irregular transversely compressed tubercles ; a broad no- 

 dulus, elevated, somewhat double ridge extending from 

 the beaks to the anterior basal edge, and projecting on 

 that part ; a broad furrow or wave behind the ridge end- 

 ing in the emarginate basal edge, and a furrow before 

 separating the anterior hinge and anterior dorsal margin : 

 cardinal teeth sulcated : lateral tooth striated, rough, and 

 in the left valve somewiiat double : posterior muscular 

 impression deep and partly rough : cavity of the beaks slU' 

 gular, compressed and directed backward under the car- 

 dinal tooth : 7iaker pearly white, and on the fore part iri- 

 descent. 



OBSERVATIONS. 



The above is Barnes' description of this strongly mark- 

 ed, common species. It is an inhabitant of the Ohio and 

 its tributaries, and approximates, by its varieties to some 

 of the varieties of U. bullatus, Raf. Barnes compares it 

 with the U. verrucosus, Kaf., to which, however, it has 

 but a remote affinity. 1 have received specimens from 

 Dr. Hildreth of Marietta and Mr. Barabino of New-Or- 

 leans. The impressions of the plate, with Barnes' name 

 of rugosus, w^ere colored before I received the '-Monograph 

 of the Bivalve shells of the Ohio," the faithful translation 

 of which, Mr. Poulson presented to me. 



REFERENCE TO THE PLATE. 



The internal, external and dorsal tIow*. 

 PI. 58. 



