39 



to the eastern states. I found it in great abundance 

 in the Potomac river, near Washington, where the 

 specimens are exceedingly elongated. The smaller 

 specimen figured is a female variety from James 

 river, Virginia, where they are generally ornamented 

 with rays; the other figure represents a rare purple 

 variety from Chester river, Maryland: it is in the 

 cabinet of Mr. Phillips. In old shells the teeth are 

 often thick and direct. 



UNIO ICTERINUS. 



Plate XVIII.— Fig. 2. 



DESCRIPTION. 



Shell elliptical, moderately thick; anterior margin 

 regularly rounded; posterior margin descending ob- 

 liquely, and subtruncated at the extremity; umbo not 

 prominent; summit decorticated; umbonial slope very 

 oblique, angulated; epidermis smooth and polished, 

 olive yellow; within salmon coloured; cardinal tooth 

 in the left valve trifid, in the right, single. 



SYNONYME. 



U. icterinus, Nob. New fresh water shells, p. 41. pi. vi. fig. 5. 

 Cab. Ji. N. S. No. 2106. 



OBSERVATIONS. 



I found the species in the Savannah river, at Au- 

 gusta. It resembles U. lanceolatus in epidermis and 

 colour. Its proper place, we think, is between nasn- 

 tus and declivis^ Say. 



