﻿336 PTYCflOnRANCHUS 



Type locality, Archie's Fork of the Little Red River, Clinton, 

 Ark. 

 Ptychobraitchus clintonensis Simpson, Pr. Ac. N. Sci. Phila., 



1900, p. 79, pi. V, fig. 3; Syn., 1900, p. 613. 



Quite variable in outline, a large series of shells from the 

 type locality includes long ovate, long elliptical, and slightly 

 obovate forms, and a few of the older ones are a little arcuate. 

 Some of the specimens very closely resemble Unio gibbosus, 

 but the pattern of delicate wavy rays seems to be constant and 

 is very dififerent from anythitig I have seen in that species. 

 The animal is different, and the gravid female has the wonder- 

 fully folded marsupium occupying the entire outer gills, as in 

 P. phaseohis, foremanianum, etc. 



Ptychobranchus foremanianum (Lea). 



Shell exceedingly variable in form, more or less inequilat- 

 eral, short to long triangular, scarcely subinBated to inflated, 

 wide and rounded or narrow and pointed behind, with high, 

 rather full beaks, their sculpture not seen ; posterior ridge well 

 developed, often single though occasionally somewhat double ; 

 rest periods often marked by a concentric groove, which some- 

 times shows as a dark line ; surface pale dirty yellow, tawny 

 or yellowish-green, generally with more or less broken rays ; 

 sometimes these are wavy and nearly entire, again they may 

 appear as squarish spots or the two patterns may be combined 

 in one shell ; often the whole surface is entirely rayless ; left 

 valve with two pseudocardinals and two laterals ; right valve 

 with one pseudocardinal and one double lateral ; beak cavities 

 shallow ■ nacre white, sometimes tinted buff, often thicker in 

 front. 



Length 62, height 36, diam. 23 mm. 



Length 53, height 35, diam. 26 mm. 



Length 46, heigltt 32, diam. 21 mm. 



Length 57, height 35, diam. 20 mm. 



Alabama River drainage. 



Type locality, Coosa River, Ala. 



