32-4 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 (Pseudoon) castanea (Lea). 44 

 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 21, 1911. 



Identical in all essential respects with 0. 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 0. 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 genus at 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, 19006, p. 602) who have discussed this species, emphasize 

 its similarity to 0. ellipsis. Lea's words: "This small species is allied to U. cir cuius 

 (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 



