UNIO 605 
horizontal or slightly up-curved; epidermis thick, chestnut to 
blackish; left valve with two strong, rough pseudocardinals 
and two laterals; right valve with one pseudocardinal, a ves- 
tigial one above it and sometimes traces of a third behind, with 
one granular lateral, which often shows vertical striation ; 
beak cavities shallow, with a few scars; anterior cicatrices deep 
and smooth; nacre whitish-violet or bronzy-tinted, iridescent 
behind. 
Length 120, height 75, diam. 46 mm. 
Chattahoochee and Flint rivers, Georgia. 
Type locality, Chattahoochee River, Ga. 
Unio sloatianus Lea, Pr. Am. Phil. Soc., I, 1840, p. 287; Tr. 
Ame Phils See, VET, 1842, p. 217; ple xvi, fig: 33; Obs., IT, 
1842, p. 55, pl. xvi, fig. 33—CuHeENu, Ill. Conch. 1858, pl. 
XXxII, figs. 7, 7a, 7b.—KustTER, Conch. Cab., 1862, p. 286, 
pl. xevr, fig. 3—SIMPson, Syn., 1900, p. 705. 
Margaron (Unio) sloatianus Lea, Syn., 1852, p. 21; 1870, p. 
aE: 
Plectomerus sloatianus Conrap, Pr. Ac. N. Sci. Phila., VI, 
195 3;0p) 201. 
Unio atromarginatus Lea, Pr. Am. Phil. Soc., I, 1840, p. 288; 
eer. Ihe soc. Vv lil, 1642) p, 207, pi. xiii, fig. 21; Obs. 
III, 1842, p. 45, pl. x1, fig. 21.—CneEnu, Ill. Conch., 1858, 
pl. xxvii, figs. 6, 6a, 6b.—Kuster, Conch. Cab. Unio, 1861, 
Pe 250, PlLaLeXxiv, fio. 2. 
Margaron (Unio) atromarginatus Lia, Syn., 1852, p. 19; 1870, 
Pp. 20. 
Plectomerus atromarginatus ConraAp, Pr. Ac. N. Sci. Phila. 
WI. 1853; p.260. 
Umio aratus Conran, Ann. and Mag., IV, 1849, p. 302. 
Unio plectophorus Conrap, Jl. Ac. N. Sci. Phila., I, 1850, p. 
277 pl SRRVIL, fig. :7: 
Plectomerus plectophorus Conran, Pr. Ac. N. Sci., Phila., VI, 
Te53, p. 2. 
A fine, robust shell, which superficially resembled the Unio 
trapezoides of Lea, but which, I am convinced, is not closely 
related to it. The external sculpture of the two is really quite 
