147 St. Maurice and Claiborne Pelecypoda 147 



De Gregorio pointed out the impropriety of using the name 

 disco/dah's ior this shell and the lack of agreement of Conrad's 

 descri])tion with the trigoniata of Lea. 



This is a middle Eocene species becoming most characteris- 

 tically developed in the Jackson beds of Arkansas. 



St. Maurice and Claiborne localities. — Claiborne Bluff, the 

 "sand bed" and the St. Maurice claj-s at the base of the bluff ; 

 Hamilton Bluff, Ala. ; Ft. Gaines, Ga. ; 5 miles N. of Orange- 

 burg, S. C. 



Meretrix trigoniata var. winnensis, n. var., PI. 46, Figs. 9-13 • 



Varietal differentiation.— OenQr3.l form somewhat trigonal 

 and very inflated, as shown by the figures ; surface with concen- 

 tric lines and undulations, stronger near the anterior and basal 

 margins, and with exceedingly fine concentric striae superim- 

 posed ; apparently when slightly eroded, showing radii crossing 

 the lines of growth at right angles, hence turning upwards pos- 

 teriorly {Cai77ptonectes-l\ke) recalling in this region the markings 

 on some species of Circe ; as in trigoniata, a trace of an obsolete 

 channel radiating from beak to base just anterior to the umbonal 

 ridge ; lunule as broad, but shorter than in trigoniata ; anterior 

 tooth comparatively longer but less pronounced than in trigoni- 

 ata, pallial sinus not deep, pointed ; lines of growth not so even, 

 regular and deeply incised as in trigoniata ; substance of the 

 shell thinner, margin often crenulate ; some forms as in figs. 11, 

 12 and 13 exceedingly inflated, reminding one of Sphcerella. 



In the most inflated forms there is not a trace of radii nor 

 of marginal crenulation but we are inclined to regard this as a 

 minor variation from the typical forms. 



The outline of this variety is much more triangular than 

 that of hatchitigbeensis, the shell is much thinner and the teeth 

 are different. The globose form, shorter lunule and exterior 

 markings serve to differentiate it from trigoniata, s. s. 



The specimens we have, though numerous, are all in the 

 form of casts and impres.sions in a red, fine-grained, hard, sandy 



