67 

 UNIO POLITUS. 



Plate XXXVII.— Fig. 2. 



DESCRIPTION. 



Shell suborbicular, convex, with slight concentric 

 furrows; anterior margin obtusely rounded; posterior 

 margin nearly direct; ligament margin rectilinear, 

 slightly declining; umbonial slope rounded; disks flat- 

 tened or very indistinctly furrowed posteriorly; basal 

 margin rounded, or slightly gibbous in the middle; 

 epidermis glossy, with fine concentric wrinkles; umbo 

 prominent, smooth and polished, with dark green 

 interrupted rays; within white; cardinal teeth thick, 

 very direct. 



SYNONYMES. 



U. politus, Say. Araer. Conch., No. 6. 



U. subrotundus, Lea. Trans. Amer. Phil. Soc, new series, vol. 



iv. p. 117, pi. xviii. fig. 45. 

 Cab. A. N. S. No. 20409. 



OBSERVATIONS. 



Related to U. Kirtlandicus, Lea, from which it dif- 

 fers in being proportionally more elevated and much 

 less compressed. It is also a smaller species. The 

 name of subrotundus has necessarily been abandoned, 

 as it is preoccupied for a different species. 



