132 



rounded : anterior margin rounded, or veiy obtusely angulated : 

 umbo elevated : fosset behind tbe beaks, moderate, wider tban 

 long, not angulated behind : disk deeply wrinkled or undulated 

 with a series of transverse elevations, sometimes separated by small 

 longitudinal lines, so as to resemble, as it were, drops of a liquid, 

 extending from the umbo to the base : within white : teeth direct. " 



Length, about two inches and nine-tenths; breadth, three 

 inches and seven-tenths. Convexity, nearly two inches. Inhabits 

 Wabash. 



A common species, distinguishable by the single series of trans- 

 verse elevations on the middle. The allied species are U. cardice 

 and mcurvis, nob.*; but besides other characters, it may be dis- 

 tinguished from either by the less prominent nates, the smaller 

 fosset, and the series of the disc. Amongst the numerous species 

 sent to me by Mr. Barnes, previously to the publication of his 

 paper, was a small valve of this species, but it was then referred 

 as a variety to the convenient but obsolete receptacle of this 

 genus, U. cr-assus. 



Unio velum. — Transversely elongate suboval, compressed, very 

 fragile and thin, olivaceous, radiated with green ; umbo not 

 prominent, placed far backward ; base subrectilinear ; anterior mar- 

 gin more widely rounded in the posterior margin, with prominent 

 membrane, erenate at its tip ; within margined with opake white ; 

 primary teeth, a conic one in the left valve, with a recipient sinus 

 in the right valve ; lateral teeth simple and single in each valve. 



Length, more than half an inch ; breadth, less than one inch and 

 one-fifth. Inhabits the Kentucky River. 



This pretty species is remarkable in having the epidermis ex- 

 tended into a broad, erenate membrane, terminating the anterior 

 margin. In the form of the teeth and the white interior margin 

 this shell resembles the U. monodonta ; and, in fact, I was led 

 from these characters to suppose it the young of that shell, but 

 afterwards finding the young, and perceiving that the umbo was 



* I think these two species have long since been published under the 

 names of corduta and intorta. I therefore suppress the descriptions here. 

 I may remark, further, that the descriptions of Unio here given were 

 chiefly made about three years since, together with nearly twenty others, 

 which I suppressed, as the species were either anticipated or subse- 

 quently made known in the works of recent naturalists. 



