OQUADRULA 859 
per end of the truncation slightly angled; posterior ridge full, 
widely rounded; surface more or less covered with low pus- 
tules, taking the form on the dorsal slope of nodular, curved 
ridges ; epidermis lurid or ashy-brownish; pseudocardinals ra- 
dial, rather smooth, two in the left valve and a single or 
double one in the right: beak cavities very deep, compressed ; 
muscle scars large and deep; nacre dull, lurid whitish. 
Length 60, height 53, diam. 30 mm. 
Alabama and Black Warrior Rivers, Alabama. 
Type locality, Alabama River. 
Umio vallatus Lea, Pr. Ac. N. Sci. Phila., XII, 1868, p. 45; Jl- 
We: Ns sci Phila., 1860, .p. 315, pl. a, fig: 128; Obs:, XI, 
LOGO. P75) Pls L, fig. 128: 
Margaron (Unio) vallatus Lea, Syn., 1870, p. 34. 
Quadrula vallata SIMPSON, Syn., 1900, p. 782. 
Not so quadrate of cahabensis, more inflated, solider and 
duller colored throughout. Yet it is quite probable that the 
two species run together. 
QUADRULA HOUSTONENS!IS (Lea). 
Shell subrhomboid or subquadrate, inflated, solid, nearly or 
quite equilateral; beaks full and high, turned forward over a 
lunule; posterior ridge well developed, narrowly rounded or 
subangular, ending at or near the base in a blunt point; an- 
terior end rounded, sometimes slightly slopingly truncate 
above ; base line curved or nearly straight ; posterior end near- 
ly or quite squarely truncated; surface usually free from pus- 
tules, rarely having a few feeble ones; epidermis yellowish- 
green in young shells, sometimes faintly rayed, becoming ashy 
brown or lurid brown when old; pseudocardinals strong, ofte: 
split up: left valve with two laterals; right valve with a single 
or somewhat double one; beak cavities deep; muscle scars 
large, impressed; nacre silvery white. 
Length 66, height 59, diam. 38 mm. 
Texas and southern Arkansas. Verdigris River, Kansas? 
Type locality, Houston and Rutersville, Texas. 
