30 THE NAUTILUS. 



the type-locality on June 7, 1912, and proved to be a gravid 

 female, with the glochidia fully developed. The others were 

 found about 7 or 8 miles below in North River, above Buena 

 Vista, Rockbridge Co., Va. : 2 males, 2 sterile, and 2 gravid 

 females, one of the latter with eggs, the other with the glo- 

 chidia just beginning to form. The largest is a male, length 

 40.5, height 27.5, diameter 13.5 mm., the next largest, a female, 

 measures, length 40, height 27, diameter 15 mm. 



The shape of the shell is somewhat variable : Conrad's figure 

 represents a rather long specimen ; I have such specimens, but 

 others are shorter. The figure shows no trace of rays, but 

 sometimes these are rather distinct. 



In Simpson's system (1. c., pp. 719-720), this species forms 

 the group of U. striatulus, together with three others: stria- 

 tulus Lea, amabilis Lea, and brimleyi Wright. I have no 

 doubt that these are indeed closely allied, and should not be 

 astonished, if they finally should prove to be all the same spe- 

 cies. Of striatulus and brimleyi I am rather strongly inclined 

 to think that is the case. 



The essential characters of the soft parts have been men- 

 tioned in the description of the genus. It should be noted 

 that the mantle connection between anal and supraanal is 

 present in all of my specimens, and although shorter than the 

 anal, is better developed than in the species of Fusconaja, 

 Quadrula, Plethobasus, and Pleurobema. The comparatively 

 distinct papillae of the anal should also be noted. 



The color of the abdominal sac and the gills is grayish- 

 white; foot paler or darker orange, adductors pale orange. 

 The charged outer gills of the gravid female are bright red 

 (like those of Fusconaja rubiginosa) . Also the gonads are 

 red. Placentae subcyliudrical, sometimes very slightly com- 

 pressed, but only near the base ; they are rather solid and can 

 easily be taken out entire, even when glochidia are present. 



Glochidia semielliptical, without hooks. Length and height 

 the same, 0.18 mm. 



PLEUROBEMA FRIERSONI (B. H. Wright) (See: Quadrula fr. 

 Simpson, 1900, p. 787). 



A number of specimens of typical friersoni were received 



