UNIO 701 
Lampsilis poper Pirspry, Pr. Ac. Nat. Sci. Phila., 1909, p. 535. 
Elliptio popet ORTMANN, Ann. Car. Mus., VIII, 1912, p. 271. 
? Unio vere-pacis Tristam, P. Z. S. Lond. 1863, Pt. 3, p. 414. 
—Simpeson, Syn., 1900, p. 738. 
Unio ravistellus var. vere-pacis VON Marvrerns, Biol. Cent. 
ineT.,. WOU TOO1,: py i520; pl: ReRVIIT, figs; 1, 14. 
The greatest diameter of this shell is at or a little behind the 
center; from this point there is a gradual and nearly straight 
slope to near the anterior end, from which place it rapidly 
narrows to the anterior point. I have examined gravid fe- 
males of this species and the marsupium occupies the entire 
outer gills. ‘This form differs from U. poeyanus in being 
wider behind and darker colored. Its beaks are much more 
strongly sculptured. 
Unio vere-pacis Tristam is probably a synonym. 
UNIO POKYANUS Lea. 
Shell elongated, inequilateral, scarcely, if at all, narrower 
in front, convex, subsolid, with a low, rather rounded poste- 
rior ridge, which is hardly biangulate; beaks rather low but 
sharp, their sculpture consisting of very faint ridges; dorsal 
line nearly straight; basal line straight or slightly incurved at 
the middle, parallel with the dorsal line; anterior end rounded ; 
posterior end rounded below, obliquely subtruncate above ; 
epidermis straw-colored in young shells, becoming faint brown- 
ish-green, often banded with yellowish, in older shells, some- 
times feebly rayed and suicate; left valve with two subcom- 
pressed pseudocardinals, the hinder reflexed, and two feeble 
laterals; right valve with one pseudocardinal and one lateral ; 
beak cavities and muscle sears shallow ; nacre whitish. 
Length 55, height 23, diam. 15 mm. 
Rio de las Balsas, near Coyucan, Mexico. 
Unio poeyanus Lea, Pr. Ac. N. Sci. Phila., [X, 1857, p. 85; 
Ome. = V1, 1857. p- 35, pl. xxx, fio. 30.5 Jl. Ac. N. Sci. Phila, 
III, 1858, p. 315, pl. Xxx, fig. 30.—Sowersy, Conch. Icon., 
XVI, 1868, pl. xc, fig. 486.—Srmpson, Syn., 1900, p. 738. 
_ 
Margaron (Unio) poeyanus Lea, Syn., 1870, p. 57. 
