35 
affinity than with any other species. It appears to 
be destitute of rays. 
This is the only Unio of a suborbicular form yet 
discovered in the Atlantic rivers. I have only two 
specimens, the ffirgest of which is figured. 
I have given this shell the name of my kind friend, 
Mr. William Mason, one of the earliest American 
Conchologists, whose discoveries have enriched our 
•cabinets with many new and rare species of land and 
fresh water shells. 
UNIO DELUMBIS, 
Plate V. — Fig. 3. 
DESCRIPTION. 
Shell ovate, elongated, very thin and fragile, veil- 
tricose; ligament margin slightly elevated; anterior 
side rather narrow, posterior margin rounded; epi- 
dermis olivaceous, with green rays; umbonial slope 
rounded; margin of the ligament slope rounded, very 
oblique; within bluish, highly iridescent; cardinal 
teeth laminar; cavity capacious, 
OBSERVATIONS. 
I found this shell abundantly near Cooper river, 
South Carolina, in the small streams; it is more 
nearly allied to U. ochraceus, of Say, than to any 
other species; but it may be distinguished by its el on- 
