QUADRULA 887 
and wide; between it and the posterior ridge there is generally 
a radial depression; surface with irregular growth lines; epi- 
dermis cloth-like, reddish-brown, dull and rather rough; pseu- 
docardinals radial, somewhat split up; lateral of the right valve 
more or less double; beak cavities deep, compressed; muscle 
scars small, deep; nacre white, thinner and iridescent at the 
posterior base. 
Length 54, height 6o, diam. 38 mm. 
Length 50, height 53, diam. 33 mm. 
Ohio, Cumberland, and Tennessee River systems ; southwest 
to Kansas and Arkansas. 
Type locality, Ohio River, Cincinnati, Ohio. 
Unio plenus Ura, Pr. Am. Phil. Soc. 1, 1840, p. 286; Tr. Am. 
Pink Socy VEIT, 1843, p21, pl. xy Ge: 26; Obs., I, 1842. 
p- 49, pl. xtv, fig. 26.—Kusrer, Conch. Cab., 1861, p. 264, pl. 
LXXXJX, fig. 3—Sowersy, Conch. Icon., XVI, 1868, pl. 
ET ho. 205. 
Margaron (Unio) plenus Les, Syn., 1852, p. 25; 1870, p. 39- 
Quadrula plena Stupson, Syn., 1900, p. 790. 
Close to several species, yet probably as distinct as any 
member of the group. It is usually a little higher than wide 
and in this character it differs from obliqua and solida. ‘The 
epidermis is rougher and more cloth-like than in any allied 
species. The post-basal point is short and never drawn out as 
it is in solida or pyranudata. 
QUADRULA FLEXUOSA Simpson. 
Shell subtriangular, solid, inflated with a feebly double pos- 
terior ridge, which ends in a blunt point or slight biangulation 
at the base of the shell, inequilateral; beaks high and rather 
full, badly eroded in the only shell seen; anterior end rounded ; 
base line nearly straight, slightly sinused at the lower end of 
a wide, radiating depression in front of the posterior ridge; 
outline of dorsal slope almost evenly curved; epidermis rough- 
ly, concentrically striate, tawny to brownish, showing the rest 
marks ; hinge plate wide and flat ; pseudocardinals low, diverg- 
ing, ragged; laterals straight, short, that of the right valve 
