OBSERVATIONS. 



In general outline this shell has some resemblance to U. 

 purpuretis,* Nob. ; but it is distinguished by many charac- 

 ers, and more obviously by the character of the anterior 

 costated margin. It is a native of South Carolina and was 

 sent to me by Professor Vanuxen, w^ho obtained it from 

 the North fork of the Holstein river. 



REFERENCE TO THE PLATE. 



Upper figure, exterior of a valve. 

 Middle figure, back of the shell. 

 Lower figure, interior of a valve. 

 PILATE XV. 



* Although Mr. Lamarck quotes the proper name of this species as a synonym, 

 yet he has by some error changed it to purpurascens. That it is an error is to 

 be inferred from the observation under his description of U. cariniftra, where 

 he says, "tr6s-distinct de I'U. purp-urea." 



