30 



interrupted undulations, which are profound behind 

 the umbonial slope; surface rough, with distant slight 

 concentric grooves; umbones much flattened, beaks 

 prominent; epidermis dark olive, and obscurely ray- 

 ed; cardinal and lateral teeth thick; anterior and pos- 

 terior muscular impressions profound; nacre pearly 

 white and iridescent. 



Unio ccelatus, nob. Silliman's Journal, vol. xxv. p. 

 338, pi. i. fig. 2. 



OBSERVATIONS. 



This is a remarkable and very distinct species, 

 similar in outline to U. lineolatus, Raf. It differs 

 from all its congeners in the singular manner in 

 which its undulations are disposed. It is nearly as 

 much compressed as U. lineolatus. The epidermis 

 in some specimens is almost black. It inhabits Ten- 

 nessee, Elk and Flint rivers, and is rare. 



UNIOMACULATUS. 



Plate YV.—Fig. 4. 



DESCRIPTION. 



Shell subtriangular, compressed; valves moderate- 

 ly thick; epidermis much wrinkled, except on the um- 

 bones, which are smooth; brown olive, with a few 

 very broad, and narrow intervening interrupted 

 green rays; beaks prominent; a slight and broad fur- 

 row extending obliquely from the beaks to the base; 

 umbonial slope subangulated, behind which the shell 

 is cuneiform; ligament margin oblique, rectilinear; 



