312 Annals of the Carnegie Museum. 



According to its known affinities and the gill-structure, this species 

 should be bradytictic, and not tachytictic, as Lefevre and Curtis 

 believe. But its primitive character makes it appear possible that 

 in its breeding habits it may also be primitive, although I do not 

 believe that it is a characteristic tachytictic form, for it possesses 

 adaptations to a long breeding season. 



Genus Cyprogenia Agassiz. (1852.) 

 (Simpson, 1900ft, p. 609.) 



Shell rounded-triangular, inflated, often with a posterior ridge and a 

 depression in front of it (especially in the young shell). Disk with 

 nodular sculpture. Beak-sculpture obsolete (according to Simpson) 

 slightly double-looped. 37 Epidermis greenish-yellow, painted with 

 delicate rays, which break up into mottlings and spots. Male and 

 female shell alike. 



Inner lamina of inner gills free from abdominal sac, except at 

 anterior end. Edge of mantle in front of branchial with fine crenu- 

 lations, which soon disappear anteriorly, but without special structures. 

 Marsupium consisting of rather few (generally less than ten) ovisacs, 

 lying in the center, or a little before the center, of the outer gills. 

 The ovisacs begin near the base of the gill, and reach far beyond the 

 edge. They are extremely long, and coil up spirally, in a backward 

 and inward direction. The placentae are very solid, subcylindrical 

 like the ovisacs, and spiral. Glochidia distributed all through the 

 placental mass, of medium size, almost semicircular. 



Type C. irrorata (Lea). 



The structure of this genus can easily be traced back to Obliquaria. 

 The same general plan is observed in the structure of the soft parts, 

 except that the marsupium is unusually elongated, and, in order to 

 be accommodated in the shell, it is coiled up. 



Cyprogenia irrorata (Lea). 



I collected, September 24, 1910, two males and one gravid female 

 in the Ohio River at Portsmouth, Scioto Co., Ohio, and received from 

 B. Walker, three gravid females from the Cumberland River in 

 Cumberland Co., Kentucky. 



No particulars as to the breeding season are known, but my specimen 



37 Although I have several specimens with tolerably well preserved beaks, I 

 have never seen the beak-sculpture clearly. 



