876 QUADRULA 
I hardly see why Dr. Jlea made two species out of this form 
which is reasonably constant in its characters. It is shaped 
something like Q. cerina but is strongly, concentrically ridged. 
It is more evenly quadrate and more strongly sculptured than 
rubiginosa. 
The shell reported under the name Unio negatus, from Kan- 
sas, is probably a somewhat sulcate rubiginosa. 
QUADRULA RUBIDULA Frierson. 
“Shell small, heavy, somewhat triangular; base emarginate ; 
dorsum arched; posterior angle biangulate ; ligament elevated, 
light red. Beaks not very high; umbones inflated; sides flat- 
tened; epidermis brown, rough, obsoletely raved and showing 
traces of a greenish tint. Cardinals stout, short, rough, in- 
clined to be double in both valves; laterals rather short, heavy, 
rough and slightly curved; cavity of shell very irregular, ex- 
cavated from beak to posterior margin; beak cavity deep and 
compressed; nacre white, sometimes pinkish, not very iride- 
Scent. 
Length 36, height 32, diam. 22 mm.” (Frierson). 
Type locality, Mulberry River; Black Warrior River and 
North River, Ala. 
Ouadrula rubidula Frierson, Naut., XIX, 1905, p. 14, pl. 1, 
figs: 324. 
“The shell is close to QO. rubida Lea and some forms resem- 
ble some of the depauperate specimens of Q. trigona Lea. 
From either of these species it may be differentiated by its 
small size and by the biangulated posterior angle.” 
QuapRULA CHUNITI (Lea). 
Shell subtriangular or subrhomboid, rather solid, inflated, 
somewhat inequilateral; beaks high and full with strong, ir- 
regular corrugations, and a few radial linze behind them; an- 
terior end rounded, somewhat obliquely truncate above ; base 
straight; dorsal slope with an angle behind the ligament, 
obliquely truncate below ; surface feebly, concentrically sculp- 
tured; epidermis brownish or greenish-brown, often faintly 
