UNIO 681 
clined to be double below, ending in a faint, wide biangulation 
at and below the median line; surface with irregular growth 
lines, sometimes having low, concentric ridges ; epidermis dark 
tawny, shaded with green, sometimes faintly rayed; base line 
nearly straight; dorsal slope obliquely subtruncated; anterior 
end rounded, usually a little narrower than the posterior end; 
left valve with low, rather blurred, double pseudocardinals and 
two laterals; right valve with somewhat double pseudocardinals 
and one lateral; muscle scars distinct; nacre dirty white or 
purplish, thicker in front. 
Length 62, height 33, diam. 19 mm. 
Length 72, height 38, diam. 24 mm. 
Type locality, Abbeville, South Carolina. Also Catawba 
River, North Carolina. 
Unio sordidus Lea, Tr. Am. Phil. Soc., X, 1852, p. 254, pl. XJ, 
fig. 1; Obs., V, 1852, p. 10, pl. xu, fig. 1—Srmpson, Syn., 
IQO00, Pp. 732. — 
Margaron (Unio) sordidus Lea, Syn., 1852, p. 33; 1870, p. 54- 
Unio gibbesianus Lea, Tr. Am. Phil. Soc., X, 1852, p. 254, pl. 
mateo Gs nV. LO52)p. £0, pl. Xil, fig. 2. 
Margaron (Unio) gibbesianus LEA, Syn., 1852, p. 33; 1870, p. 
4. 
A form or species with almost no distinguishing characters, 
yet I cannot place it with anything else. The type of U. gib- 
besianus has the pseudocardinals divided into several denti- 
Fal 
‘cles, otherwise it agrees with sordidus. The shell varies from 
subrhomboid to subelliptical, or subovate, has a dirty tawny, 
half shining, greenish epidermis and is considerably thickened 
in front. 
UNIO SPADICEUS Lea. 
Shell rather small, oblong, subrhomboid, subcompressed, 
inclined to be solid, inequilateral; beaks apparently not ele- 
vated or inflated; posterior ridge feebly double, ending behind 
in a biangulation at and below the median line; dorsal slope 
obliquely subtruncated; base line faintly emarginate in the 
middle, swollen behind that point; surface irregularly striate ; 
