25-4 Annals of the Carnegie Museum. 



Quadrula tuberculata (Barnes). 



Fifteen specimens have been investigated, collected by myself in 

 the Ohio drainage in western Pennsylvania; nine more have been re- 

 ceived from H. E. Wheeler from the Tennessee drainage in northern 

 Alabama, and the Ouachita River in Arkansas. Females are among 

 them, but not in the gravid condition. 



Simpson has created for this species the genus Tritogonia, which he 

 removed far from Quadrula. The shape of the shell is indeed somewhat 

 si range at the first glance, but it is possible, without much difficulty, 

 to correlate shape and sculpture with that of such species as lachrymosa, 

 aspera, and chiefly with certain southern forms, which probably also 

 belong here (forshei Lea, speciosa Lea, apiculata Say). 



In the structure of the soft parts, this species is essentially a Quad- 

 rula. The anal opening is separated from the supra-anal by a rather 

 short mantle-connection; the latter was found absent in one case only 

 (out of twenty-four). Branchial with well developed papillae, anal 

 with fine, but distinct crenulations, which sometimes resemble fine 

 papilla?. Inner lamina of inner gills free from abdominal sac, except 

 at its anterior end. Posterior margins of palpi connected for one-half, 

 or even more, of their length. 



Gills rather long, but also rather wide; their anterior attachment as 

 usual. Septa well developed, rather distant from each other in the 

 male. In the female they are more crowded in all four gills, and the 

 water-tubes are narrow, but there is a slight difference between the 

 inner and outer gill, the water-tubes of the former being slightly wider 

 near the base of the gills. In the marginal portion there is hardly any 

 difference in the water-tubes of the two gills (see Ortmann, 191 lb, 

 pi. 86, fig. 4). In all four gills the septa are distinctly marsupial in 

 structure: they are heavy, and have a folded epithelium. 



No gravid females have been seen by the writer, and the glochidia 

 are still unknown. 



The color of the soft parts is grayish or yellowish (or brownish) 

 white. 



Simpson (1900&, p. 608) says of his genus Tritogonia: "in the female 

 there is a thickened flap of the mantle which fills the circular posterior 

 expansion of the shell, and which has a small flap inside." I have 

 never seen anything answering to this phrase in my specimens. The 

 chief expansion of the shell is at the anal opening, and the margin of 

 this opening corresponds to it, and thus the anal is larger in the female, 



