860 QUADRULA 
Unio houstonensis Lea, Pr. Ac. N. Sci. Phila., III, 1859, p. 
£653 jl. Ac: Ny Scie Phifas, LV; 2860; ps 258 ple ne eae 
Obs., VIII, p. 40, pl. Lx, fig. 183.—Sowrrsy, Conch. Icon., 
XVI, 1868, pl. LXxxI, fig. 425. 
Margaron (Unio) houstonensis Lea, Syn., 1870, p. 55. 
Quadrula houstonensis SIMPSON, Syn., 1900, p. 782. 
A solid, inflated form with the beaks near the center. Us- 
ually the shell is entirely free from tubercles, but occasionally 
there are a few weak ones. It is not so smooth as petrina 
and the epidermis is duller colored. 
QUAPRULA PETRINA (Gould). 
Shell subelliptical, subquadrate or subrhomboid, somewhat 
inflated, slightly inequilateral, solid; beaks moderately full and 
high, turned forward over a lunule, their sculpture consisting 
of irregular corrugations, which are almost nodulous on the 
posterior ridge; posterior ridge widely rounded, sometimes 
feebly biangulate below; anterior end rounded; base line 
curved; posterior end obliquely or squarely subtruncate; um- 
bonal region corrugated; posterior slope faintly corrugately 
wrinkled, the rest of the shell smooth or very feebly corru- 
gated; epidermis rather smooth, somewhat shining, sometimes 
uniform dirty straw-color, usually yellowish-green with irreg- 
ular bands or clouds of green; pseudocardinals stumpy, trian- 
gular, two in the left valve and three in the right; beak cavi- 
ties deep, compressed; muscle scars deep, smooth; nacre sil- 
very, iridescent and thinner behind. 
length 70, height 53, diam. 32 min. 
Length 47, height 38, diam. 25 mm. 
Texas. Cragin’s localities, Verdigris and Neosho Rivers, 
Kansas, are probably erroneous. 7 
Type locality, Llanos River, Texas. 
Unio petrinus Gout, Pr. Bost. Soc. N. Hist., V, 1855, p. 228. 
Margaron (Unio) petrinus La, Syn., 1870, p. 55. 
Quadrula petrina SIMPSON, Syn., 1900, p. 783. 
More inflated, less quadrate or rhomboid than Q. aurea; less 
inflated and not so short as Q. houstonensis, and having a dif- 
ferently colored epidermis from either. 
