880 QUADRULA 
The beak sculpture of this form seems to be different from 
that of any allied species. I have never seen it perfect, but 
it is apparently oblique or zigzagged. It is longer in propor- 
tion to its height than ;iddellii, is more distinctly triangular 
than it or chunti. 
QuADRULA UNDATA (Barnes). 
Shell triangular, inflated, solid, slightly inequilateral ; beaks 
very high and full, turned forward over a lunule, their sculp- 
ture a few irregular ridges, which turn up behind and occa- 
sionally two or three rayed lire behind them; anterior end 
usually obliquely truncate above and angular in front of the 
lunule, though rarely evenly rounded; base line straight or 
lightly sinused in front of the posterior ridge; outline of dor- 
sal slope often curved, raised into a low angle behind the 
ligament; posterior ridge well developed, angled or narrowly 
rounded, ending in a blunt point at the base line; in front of 
the posterior ridge there is generally a wide, radial depression 
and in front of this is the greatest diameter; surface with 
uneven growth lines; epidermis brownish-green and_ faintly 
rayed in the young state, greenish-brown, brownish or black- 
ish in the old shell, rather dull; pseudocardinals strong, torn; 
lateral of the right valve often partly double; muscle scars. 
very deep; beak cavities moderately deep ; nacre white, salmon 
or rose-tinted, thinner behind. 
Length 87, height 70, diam. 52 mm. 
Length 85, height 74, diam. 52 mm. 
Length 50, height 50, diam. 38 mm. 
Entire Mississippi drainage; Coosa River, Alabama; Michi- 
gan and the Upper St. Lawrence drainage. 
Type locality, Wisconsin and Fox Rivers. 
Unio undatus BARNES, Am. Il. Sci., VI, 1823, p. 121, pl. rv, fig. 
A. 
Mya undata Eaton, Zool. Text book, 1826, p. 219. 
Ouadrila undata WaiKER, Naut., XXIV, 1910, p. 24, pl. 1, 
figs. 1-3; pl. 11, figs. 1-2. 
Fusconaja undata OrtTMANN, Ann. Car. Mus., VIII, 1912, p- 
241. 
