147 St. Mauricb and Claiborne' Pelecypod a 147 



De Gregorio pointed out the impropriety of using the name 

 ^z^f(?z^(3;/w for this shell and the lack of agreement of Conrad's 

 description 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 clays 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 differentiatio7i. — General form somewhat trigonal 

 and verj^ 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 {Camp t one ctes-\\\L&) recalling in this region the markings 

 on some species of Circe ; as in trigo7iiata, 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 impressions in. a red, fine-grained, hard, sandy 



