Ortmann: Families and Genera of Najades. 325 



green rays. Male and female shells differing in shape, but the dif- 

 ference often hardly noticeable. 



Soft parts agreeing with those of Obovaria in ever) respect; the 



glochidia also of the same type. 

 Type N. plicatula Charpentier. 



In its anatomical structure this genus is indistinguishable from 

 Obovaria. The differences are all in the shell. But while Obovaria 

 is primitive in its shell, Nephrdnajas inclines toward the genera of the 

 Lampsilis-type, in fact its species have been considered, at least 

 temporarily, to belong to Lampsilis. The subgenus Pseudoihi of 

 Obovaria connects this genus with Obovaria, and so we have an almost 

 complete series. 



The nomenclature of this genus is doubtful. Of the species, which 

 belong here, two (ligamentind and perdix) stand according to Simpson's 

 system in Lampsilis, and a third (sapotalensis) in Nephronajas. 

 Since Lampsilis is retained for other forms, only Nephronajas is 

 available. But the anatomy of the type species of Nephronajas 

 (plicatula) remains as yet unknown, and it is possible that it may 

 differ in anatomy from sapotalensis. In the latter case, of course, 

 Nephronajas could not be used for the present genus, and a new name 

 would have to be chosen. 



Nephronajas ligamentina (Lamarck). 



Numerous specimens from the Ohio drainage in western Penn- 

 sylvania have been investigated. In addition specimens have been 

 seen from the Ohio River in West Virginia and Ohio (collected by 

 myself), from the Cumberland River in Kentucky (var. gibba), 

 received from B. Walker, and from the Ouachita in Arkansas, received 

 from H. E. Wheeler. 



Typically bradytictic. The breeding season begins in August, and 

 specimens with eggs are present in this month and the beginning of 

 September. Later on only glochidia are observed. Specimens with 

 glochidia have again been observed in May, and the discharge must 

 take place in this month, for in June and July no gravid females 

 have ever been found, although numerous specimens have been in- 

 vestigated. 



The soft parts have been discussed by Lea (Obs., X, 1863, p. 424) 

 and Simpson (in Baker, 1898, p. 108). 



Anatomy in every particular like that of Obovaria. The inner edge 



