29 



the young shell, but subsequently, in examining a 

 number of specimens of U. congarceus from the same 

 locality, an adult specimen was discovered, which has 

 served for the figure and description. It is in Mr. 

 Phillips's cabinet. The outline of the young shell is 

 represented for comparison with that of IT. congarceus. 

 Mr. Poulson's cabinet. 



It is dedicated to Mr. William Mason, whose dis- 

 coveries have much advanced our knowledge of 

 American conchology. 



UNIO COCCLNEUS. 



Plate XIII.— Fig. 1. 



DESCRIPTION. 



Shell oblique, subtriangular, compressed, slightly 

 waved; epidermis blackish-brown, with crowded 

 wrinkles; anterior side very short; posterior side sub- 

 cuneiform, much compressed, extremity truncated; 

 umbo slightly flattened; basal margin not much ar- 

 cuated posteriorly; posterior margin slightly sinuous, 

 oblique, rounded above; umbonial slope abruptly 

 rounded; summits prominent, eroded; within salmon 

 colour, rarely white; cardinal teeth double in each 

 valve, direct. 



SYNONYME. 



U. coccineus, Hildrcth. 

 Cab. A. N. S. No. 2104. 



