63 



UNIO INTERMEDIUM 



Plate XXXV.— Fig. 2. 



DESCRIPTION. 



Shell suboval, compressed; disks flattened or slight- 

 ly furrowed from beaks to base, covered, except on 

 the posterior side, with small slightly elevated tuber- 

 cles, which are rib-shaped on the posterior slope; 

 umbonial slope not prominent, and rounded or sub- 

 angulated; posterior slope obtusely angulated; beaks 

 oblique, not prominent; ligament margin long, arcu- 

 ate; posterior margin direct, emarginate; within white; 

 cardinal teeth direct. 



OBSERVATIONS. 



Three specimens of this species were obtained by 

 Dr. S. Blanding, of Columbia, S. C, from Nolachucky 

 river, Tennessee, and were kindly submitted to my 

 inspection. They differ from the preceding in being 

 somewhat oblique, in having less prominent beaks, a 

 wider posterior slope, but particularly in being desti- 

 tute of tubercles anteriorly. From the metanevra it 

 is easily distinguished by the want of a swelled um- 

 bonial slope. It is so evident a link between these 

 two species, that I have given it the name of inter- 

 medins, suggested by my friend Mr. John Phillips. 

 In a young specimen which I have figured, the epi- 

 dermis is covered with small crowded angular green 

 spots, but in the old shell they disappear. The latter 

 becomes distinctly angulated or furrowed on the pos- 



