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. 
UNIO M4CULATUS. M V ^ 
Plate IV. — 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; 
