﻿33^ I'TYCIKn'.KANCHUS 



docardinal and one strong, somew hat double lateral ; beak cav- 

 ities shallow; muscle scars small, and deep; nacre white with 

 a deep, wide, obli(|ue furrow in the center, thicker in front. 



I^ength 50, height 34, diam. 24 mm. 



Type locality, Coosa River, Alabama. 

 Uuio triuacnis Lka, Pr. Ac. N. v^ci. I'hila., \', 1861, p. 59; JL 



Ac. N. Sci. Phila., \', 1862, p. 86, pi. xii, fig. 235; Obs., 



VIII, 1862, p. 90, pi. XII, fig. 235. — SowERisY, Conch. Icon., 



X\'I, pi. Lxxxi, fig. 428. 

 Margaron (Unio) trinacnis Lea, Syn., 1870, p. 36. 

 Ptychobranchus trinacnis Simpson, Syn., 1900, p. 614. 



T am very strongly inclined to believe that this is merely a 

 form of P. foremaniannm, but I have seen no material absolute- 

 ly connecting it. The color pattern is different from anything 

 known in that species and the single, sharp, high posterior 

 ridge, which curves down in the middle is a differential char- 

 acter. Lea speaks of the deep groove in the cavity of the shell 

 as a distinguishing feature, but the same thing, perhaps not 

 quite so strongly developed, is found in specimens of foreman- 

 ianiim. and so are the heavy, club-shaped laterals an occasional 

 character of that form. I have only seen the type. 



Ptyciioi'.ranciilis GREENi (Courad). 



Shell subtriangular, somewhat elongated, subinflated to 

 inflated, subsolid, with a rather well-developed, more or less 

 double, posterior ridge ; beaks full and high, placed nearer the 

 anterior end, their sculpture not seen; epidermis yellow or 

 tawnv, often with a few delicate rays posteriorly, subshining; 

 left valve with two small pseudocardinals and two laterals, the 

 lower club-shaped ; right valve with one pseudocardinal, with 

 occasional vestiges of another on each side of it, and one divid- 

 ed lateral ; beak cavities shallow ; muscle scars impressed ; nacre 

 whitish, a little thicker in front. 



Length 52, height 32. diam. 26 mm. 



Length 49, height 30. diam. 20 mm. 



Length 40, height 25, diam. i8 mm. 



Length 43, height 2y, diam. 15 mm. 



Black Warrior River. Alabama. 



