Ortmann; Families and Genera oi Najades. 291 



latter. Besides there is no difference whatever in the gills. The 

 slight differences mentioned cannot be regarded, under any conditions, 



as of generic value, in face of the great similarity of structure. The 

 presence of papilla? on the anal opening (Haas, io,ior/, p. no) in 

 Pseudanodonta is a character, which at most has merely specific 

 value. There remains only the glochidium (see Plate XIX. fig. 3) 

 to be considered. There are, indeed, certain differences between the 

 glochidia of A. complanata and cygnea, but as far as they are known 

 in other members of the genus and subfamily, such differences are 

 encountered elsewhere, without being considered as of generic value. 

 The glochidia are undoubtedly built upon the same plan in both species. 

 .1. complanata not only is a true Anodonta, but judging by the shape 

 of the beak and beak-sculpture belongs to that group in the genus, of 

 which .4. cygnea is the type. We cannot separate it generically from 

 the latter, without disregarding natural affinities. 



Anodonta imbecillis Say. 



1 have investigated twenty-three specimens from northwestern 

 Pennsylvania (Allegheny and Lake Erie drainages), and two from 

 Lawrence, Douglas Co., Kansas (R. L. Moodie). All were females in 

 structure, and many were gravid. This species is hermaphroditic. 



Typically bradytictic, and gravid from September to May. In 

 Lake Erie the time of discharging the glochidia is postponed even 

 further, this act having been observed as late as July 12. 



The anatomy has been described by Lea (Obs., X, 1863, p. 449). 



Of all American forms this species resembles most closely the 

 European Anodontas in the shape of the shell. It differs, however, 

 in being hermaphroditic. The soft parts present no special features, 

 and they agree both with the European A. cygnea and the North 

 American A. grandis. The anal opening is almost smooth. 



Glochidia smaller than those of cygnea, slightly higher than long 

 (length 0.30; height 0.31 mm.), of the usual shape, with hooks (see 

 Lea, Obs., VI, 1858, pi. 5, fig. 36; Ortmann, 191 lb, pi. 89, fig. 13). 



Color of soft parts whitish, foot yellowish brown; gills pale brown; 

 edge of mantle blackish. Charged marsupium brown. 



Anodonta henryana Lea. 

 Seven specimens from a branch of the Rio Grande, Mercedes, 

 Hidalgo Co., Texas, collected May 15, 1907, by Dr. D. A. Atkinson. 



