324 ANNALS OF THE CARNEGIE MUSEUM. 
Marsupium formed by about the posterior half of the outer gill, 
kidney-shaped, consisting of as many as forty and more ovisacs, its 
edge slightly pigmented. 
Glochidia similar to those of the other species. Length 0.19; 
height 0.22 mm. (see Plate XIX, fig. 11). 
Color whitish, edge of mantle inclining to blackish, chiefly in the 
region of the branchial and anal, and more intense in the male sex. 
Pigment on edge of marsupium purplish gray, not sharply marked. 
Obovaria (Pseudoén) castanea (Lea). 
Twelve males, one sterile, and five gravid females (with glochidia) 
from the Ouachita River, Arkadelphia, Clark Co., Arkansas, have been 
sent by H. E. Wheeler. They were collected on February 6 and 
March 215 T9Rx. 
Identical in all essential respects with O. ellipsis. Marsupium 
formed by twenty to thirty ovisacs and its edge not pigmented. A 
grayish streak along the inner edge of the mantle in front of the 
branchial. Glochidia of the same shape as those of O. ellipsis, but 
smaller. Length 0.15 mm.; height 0.19 mm. 
Genus NEPHRONAJAS Crosse and Fischer. (1893.) 
(Simpson, 1900), p. 591.) 
Shell ovate or subelliptical, distinctly longer than high, compressed 
or slightly inflated, without, or with, indistinct posterior ridge. Disk 
not sculptured. Beaks moderately anterior, never in the middle of 
the shell, and never very near the anterior end. Beak-sculpture 
poorly developed, consisting of a few faint bars, which have a tendency 
to become double-looped, with the central part between the loops 
obliterated. Epidermis yellowish to greenish, generally with distinct 
44 There is some doubt as to the identity of my specimens. B. Walker has a 
number of sets of a shell from Alabama, Mississippi, Louisiana, and Arkansas, 
of which he sent me specimens, and some of which have been labeled by Simpson 
castanea, but which are certainly different from the present form, and probably do 
not belong to this genusat all. Although I have not seen Lea’s type, I believe that 
I have the real castanea, for the reason that all authors (Lea, Obs., I, 1834, p. 91; 
Call, 1895, p. 9; Simpson, 1900), p. 602) who have discussed this species, emphasize 
its similarity to O. ellipsis. Lea’s words: “‘ This small species is allied to U. circulus 
(nob.) in colour and to U. ellipsis (nob.) in form”’ are entirely sufficient to recognize 
it. There is no other form known to me, of which this could be said. Also Vanatta 
(1910, pp. 102 and 103) quotes O. castanea from the Ouachita River in Arkansas, 
