QUADRULA 843) 
zigzag ridges: posterior ridge moderately developed, generally 
double, and indistinctly angled, ending at the base of the shell 
in a biangulation; in front of and behind it there is a slight 
radial depression; there is usually a more or less developed, 
median, radial elevation; surface with fine, concentric growth 
lines, otherwise nearly smooth or covered with scattered pus- 
tules; epidermis greenish in the young shell, ashy-brown in 
the adult; pseudocardinals elevated, ragged and uneven; lat- 
eral of the right valve single or slightly double; beak cavities 
moderately deep; muscle scars impressed; nacre white, often 
silvery and iridescent behind. 
Length 50, height 38, diam. 26 mm. 
Length 41, height 30, diam. 20 mm. 
Type locality, Rio Salado, New Leon, Mexico. Also south- 
western Texas. 
Umio couchianus Lea, Pr. Ac. N. Sci. Phila., IV, 1860, p. 305; 
jieAc oN oct: Piila LV. Tsbo; peis7t, (pl. UxXVie-he. TOO: 
Obs., VIII, 1860, p. 53, pl. xvi, fig. 196—Sowersy, Conch. 
Teons XV I, 1868; pl. uxxxi, fig. 420. 
Margaron (Unie) couchianus Lea, Syn., 1870, p. 54. 
Ouadrula couchiana SIMPSON, Syn., 1900, Pp. 777. 
lea has in his collection two matched pairs of this form, 
which are almost smooth. Other shells received from Dr. 
Mearns from the southwestern part of the state are more or 
less covered with scattered nodules. It is a rather small, 
somewhat elongated species having an ashy-brown epidermis. 
QUADRULA FRAGOSA (Conrad). 
Shell short, irregularly quadrate, inequilateral, subinflated, 
solid; beaks very high, full, turned forward over a well-de- 
veloped lunule; anterior end rounded; base line incurved in 
front of the posterior ridge; posterior end almost squarely 
truncated ; posterior ridge single above, double below, with a 
radial depression in front of and behind it; surface with un- 
even, concentric growth lines; anterior third of the shell other- 
wise smooth; remainder of the shell having coarse, scattered, 
irregular tubercles, which are strongest on the posterior and 
