PILEUROBEMA 805 
Unio subplanum Sowersy, Conch. Icon., XVI, 1866, pl. xuvit, 
fig. 252. 
More rhomboid and compressed than striatulum, lighter col- 
ored and less decidedly rhomboid than brimleyi. 
PLEUROBEMA BRIMLEYI (S. H. Wright). 
Shell decidedly rhomboid, convex or subinflated, somewhat 
inequiliteral; anterior end rounded but a trifle cut away be- 
low ; base Jine straight; dorsal slope obliquely truncate; dorsal 
line curved a little; beaks rather full, somewhat elevated, 
their sculpture not seen: posterior ridge full, narrowly round- 
ed; above it, separated by a shallow furrow, 1s a second slight 
ridge ; epidermis almost cloth-like, rather dull, dark dirty green- 
ish; left valve with two ragged pseudocardinals and two 
straight laterals; right valve with one pseudocardinal, and a 
faint tooth above it, with one lateral disposed to be double: 
beak cavities compressed; muscle scars shallow, small; nacre 
bluish and bluish-white, much thinner and iridescent behind. 
Length 58, height 36, diam. 21 mm. 
Type locality, Neuse River. Also Irwin’s Creek, North 
Carolina. 
Umio brimleyi S. H. Wricut, Naut., X, 1897, p. 138.—Simp- 
SON tG.wnes Netoct: Phila. 1900; pp: So; ‘pl. 1v,-fis. 6; Syn., 
1900, p. 720. 
I have seen only the type of this species, which appears to be 
perfectly distinct. It is a little more elongated than subplanum, 
to which it seems most nearly related, is more decidedly rhom- 
boid, is darker and less compressed. 
Section PLETHOBASUS Simpson, 1900. 
Plethobasus Stapson, Syn., 1900, p. 764.—ORTMANN, Ann. 
Car. Mus. VILE, 1912; p: 259. 
Shell large, irregularly oval, inflated, solid, somewhat sud- 
denly swollen at the posterior base; posterior ridge low and 
rounded; beaks rather high, near the anterior end, having a 
few strong ridges, which are curved upward behind; a row of 
low, irregular tubercles extends from near the beaks to the 
