PLEUROREMA 779 
P).2UROBEMA NUX Lea. 
Shell small, solid, inflated, inequilateral, irregularly ellipti- 
cal or ovate; beaks high and full, with two or three strong, 
irregular ridges ; anterior end evenly rounded; base line curved, 
fullest just behind the middle; outline of dorsal slope evenly 
curved or raised almost to an angle behind the ligament ; pos- 
terior ridge low but well marked, subangular or narrowly 
rounded, ending in a point at the median line; in front of it 
the shell is much swollen ; epidermis greenish-brown to reddish- 
brown, often showing the dark rest marks, almost cloth-like 
in fresh shells; pseudocardinals triangular, two in the left 
valve and one to three in the right; two laterals in the left 
valve and a somewhat double one in the right; beak cavities 
small; muscle scars impressed; nacre bluish-white, thinner 
and iridescent behind. 
Length 42, height 29, diam. 21 mm. 
Alabama River system. 
Type locality, Alabama River. 
Unio nux Lea, Tr. Am. Phil. Soc., X, 1852, p. 283, pl. xxiv, 
ne. 43; Obs., V, 1852; p: 30; pl: Xx1v, fig, 43. 
Margaron (Unio) nux Lea, Syn., 1852, p. 31; 1870, p. 49. 
Pleurobema nux SIMPSON, Syn., 1900, p. 758. 
Unio cinnamomicus Lea, Pr. Ac. N. Sci. Phila., V, 1861, p. 39; 
iaAc Ne set Phila. V 71862). p. 100; pl: xvi; fig. 248. Obs:. 
VIII, 1862, p. 104, pl. xvi, fig. 248. 
Margaron (Unio) cinnamoniinus, Lea, Syn., 1870, p. 40. 
Unio cinnamominus Sowrrry, Conch. Icon., XVI, 1868, pi 
LXXXIIt, fig. 436. 
I cannot see that cinnamomicus differs in any way except in 
having a reddish-brown epidermis. Between this and typical 
nux there is a complete blending in the matter of color. This 
differs from avellana in having a decided point on the median 
line behind. 
PLEUROBEMA JOHANNIS (Lea). 
Shell irregularly, elliptical, subrhomboid or subovate, sub- 
inflated or inflated, inequilateral, solid; beaks full and high; 
posterior ridge much less inflated than the disk in front of it. 
