188 THE AMERICAN MIDLAND NATURALIST 
nated post-ventrad with radial furrow in front of flattened post- 
umbonal ridge; beaks swollen, protruding anteriorly, sculptured 
by concentric ridges; epidermis reddish brown to black with rays 
originating in umbonal region; cardinals heavy, double in left 
single in right valve; laterals double in left, more or less double 
in right valve; nacre white. 
MISCELLANEOUS REMARKS:—The writer has been unable to 
find Pleu. obliquum in typical form anywhere in the state and 
claim is only made for it through its various forms and through 
Simpson’s report, that it is found in the Mississippi above the 
mouth of the Missouri River. Surely there is much need of re- 
search chiefly with regard to the geographic facts relating to the 
distribution of this species. Most students of geographic distribu- 
tion concur in the belief that no true obliquum is found west of the 
Mississippi and that it is rarely seen north of the Ohio. Its metrop- 
olis is that richest of all centers of mussel faunae, the Cumberland 
River, where Wilson and Clark report it as the most abundant of 
all the numerous species found there. Briefly stated, obliquum 
occurs in this state, but with its characteristic radial furrow obliterated 
and its intergrading forms are very numerous running into each 
other in every puzzling way. 
Pleurobema obliquum plenum (Lea). 
Not figured. 
1840—Unio plenus Lea, Tr. Am. Phil. Soc., I, p. 286; Tr. Am. Phil. 
Soe Will 1s43) py 200, DInoeVi hg.26) 
1900b—Quadrula plena Simpson, Proc. U. S$. Nat. Mus., p. 790. 
The writer has not found this species in this state and no 
description appears here, since neither soft parts nor shells have 
been seen. However, plenum is listed as a variety for Missouri 
through the kind report of Mr. Walker that he has it from the 
James River, near Springfield, and that it bears the same relation 
to obliquum as does also a variety of coccineum found in the same 
locality. 
Pleurobema obliquum pyramidatum (Lea). 
(‘‘ Pig-toe,’’ “Pyramid Pig-toe.’’) 
PIXXX, LIS se. AsGua Go. 
1834— Unio pryramidatus Lea, Tr. Am. Phil. Soc., IV, p. 109, pl. XVI, 
Hees O ° 
1900b—Quadrula pyramidata Simpson, Proc. U. S. Nat. Mus., XXII, 
p. 790. 
