Ortmann: Families \\i> Genera oi Najades. 



249 



and a female from Ouachita River, Arkadelphia, (.'lark Co., Arkansas. 

 None of the females was gravid. 



The description of the sofl parts given by Lea (Obs., X, 1863, p. 436) 

 is incomplete. 



The anal opening is separated from the supra-anal by a moderately 

 long connection of the margins of the mantle, which varies slightly, 

 and is a little longer than the anal, but always much shorter than the 

 supra-anal. In two cases this connection was absent. Branchial 

 with well developed papillae, anal with minute papillae. Inner lamina 

 of inner gills free, except at the anterior end. Posterior margins of 

 palpi connected for about one-half of their length. 



mp 



mp 



Fig. 5a. Left gills of a sterile female of C. trapezoides, from Pearl River, Jackson, 

 Hinds Co., Miss. (Cam. Mus., No. 61, 4,924.) 



Septa of the gills of the male rather distant from each other, and 

 water-tubes wide. In the female the septa are much more crowded, 

 and the water-tubes are narrow, chiefly so in the outer gill. In the 

 inner gill of the female, near the base, the septa are a little more distant, 

 but toward the edge they become more crowded by intercalation of 

 additional ones, so that in the marginal half of this gill the water- 

 tubes are almost as narrow as those of the outer gill. Altogether the 

 marsupial character of the crowded septa is not so distinctly pro- 

 aounced in the inner gill, although all four gills are built to receive 

 eggs and to serve as marsupia, a fact, which is evidenced by the struc- 



