﻿332 PTYCHOBRANCHUS 



Tliis rcniarkalilc species does not appear to l)e closely related 

 to any living form. The shells hear some resemhlance to those 

 of certain males of TrunciUa pcrplcxa, hut in that species the 

 female shells differ remarkahly from those of O. reflexa. The 

 knobs in this species are more pinched up and larger than they 

 are in 7'. pcrplexa and the shell is shorter. 



I am sorry to have to place the very appropriate and well- 

 known name of Barnes in the synonymy, but I believe that the 

 description of Rafinesqne for his Obliquaria reflexa defines 

 this species and nothing else, and although it is not figured, 

 I feel justified in using his name. 



PTYCHOGEN^. 



Male and female shells essentially alike ; embryos contained 

 in distinct ovisacs with rounded bases, occupying the entire 

 outer gills, which, wben gravid, consist of a series of folds. 



Genus PTYCHOBRANCHUS Simpson, 1900. 



Ptychobranclms Simpson, Pr. Ac. N. Sci. Phila., 1900, p. 79. 

 — Ortmann, Ann. Car. Mus., VIH, 1912, p. 305. 



Shell triangular, solid, sometimes becoming arcuate in old 

 specimens, umbonal region rather elevated ; beak sculpture 

 consisting of faint, somewhat broken ridges; which have a 

 tendency to be doubly looped ; i)osterior ridge rounded but well 

 developed ; epidermis usually painted with wavy, hair-line 

 rays or broken, radiating bars, which show a tendency to form 

 square spots ; hinge plate rather wide and flat ; pseudocardinals 

 small, low, triangular and roughened ; laterals club-shaped, 

 remote; cavity of the beaks shallow; muscle scars rather deep. 

 Animal having the inner gills free all or part of their length 

 from the abdominal sac ; marsupium occupying the basal half 

 of the whole length of the outer gills and hanging in from 

 six to twenty beautiful folds; ovisacs distinct, each ending be- 

 low in an enlarged, rounded bulb, which has a colored spot 

 in its center; mantle thin, with a dark, thickened border; 



