V N I O . 



U. cicatricosus. Shell, trans vers civ subovatc: posterior mar- 

 gin very short, hardly extending beyond the beaks, regularly 

 rounded: anterior margin rounded, or very obtusely angulated: 

 umbo, elevated: fosset, behind the beaks, moderate, wider than 

 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. In- 

 habits Wabash. 



A common species, distinguishable by the single scries of 

 transverse elevations on the middle. The allied spee'es are 

 U. rarii~e and incurvus, Nob.*; but, besides other characters, 

 it may be distinguished from cither 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 *\r. 

 but it was then referred as a variety to the convenient but ob- 

 solete receptacle of this genus, U. crassus. 



U. velum. Transversely elongate suboval, compressed, very 

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

 prominent, placed far backward; 6ase, subrectilincar; anterior 

 margin, more widely rounded in the posterior margin, with a 

 prominent membrane, crenatc, 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; lulcral teeth, simple and 

 single in each valve. 



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

 and one fifth. Inhabits Kentucky River. 



This pretty species is remarkable in having the epidermis 

 extended into a broad, crenate membrane, terminating the 

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

 interior margin, this shell resembles the I . , and, 



in fact, I was led from these chai <o suppose it the young 



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

 eoru'.i rta. 1 thi n for* 



further, thai the , 



th r » nli nearly ti 

 were either anticipated or si known in th 



alitor:. 



