770 PLEUROBEMA 
PLEUROBEMA TROSCHELIANUM (Lea). 
Shell irregularly elliptical, subtiiangular or subovate, some- 
what inflated, rather solid; beaks full, rather high and round- 
ed, placed near the anterior end; anterior end rounded or 
slightly obliquely truncate above; base and dorsal outlines 
rounded, the Jatter sometimes raised almost to an angle behind 
the ligament; posterior ridge well developed, narrowly round- 
ed, slightly double below, ending near the base in a faint bian- 
gulation ; epidermis tawny to dirty greenish-brown, sometimes 
with a single, broken ray near the posterior ridge; pseudocar- 
dinals small, stumpy; two in the left valve and one to three 
in the right: iaterals two in the left valve and a double one in 
the right; beak cavities shallow ; muscle scars small, impress- 
ed; nacre whitish, thinner and iridescent behind. 
Length 4o, height 28, diam. 21 mm. 
Alabama River system. 
Type locality, Coosawattee River, Murray Co., Ga. 
Unio troschelianus Lua, Tr. Am. Phil. Soc., X, 1852, p. 280, 
ply Xxim, fig’ 390: VObs.,. Vo18525p. 30). pl Soxtiiee ao: 
Margaron (Unio) troschelianius Lea, Syn., 1852, p. 26; 1870, 
p. 40. 
Pleurobema troscheliana SIMPSON, Syn., 1900, p. 750. 
Close to stabile, but less inflated, less solid, having a stronger 
posterior ridge and a darker epidermis with a tint of dirty 
green. It is more elongated than irrasum or alium. 
PLEUROBEMA JRRASUM (Lea). 
Shell subtriangular, short, rather inflated, solid, slightly in- 
equilateral; beaks full, high, rounded; anterior’ end rounded. 
slightly obliquely truncate above; base line rounded; outline 
of dorsal slope somewhat curved, elevated into a low angle 
behind the ligament; posterior ridge well developed, narrowly 
rounded, ending in a rounded point below the median line ; epi- 
dermis dirty greenish-brown, rarely with vestiges of rays; 
pseudocardinals subtriangular, two in the left valve, one to 
three in the right; laterals short, two in the left valve and a 
