324 PROCEEDINGS OF THE ACADEMY OF 



SEDGWICKIA? COMPRESSA, Meek. 



Anatina simiata, James, 1871. Catalogue Fossils Cincinnati Group, p. 12. 

 (Not Anatina? simiata, Hall.) 



Shell longitudinally oval, compressed, about one-fourth longer 

 than high, cuneate posteriori)^, and more convex in the central 

 and anterior regions, with a slight concavity descending from the 

 beak to the base of each valve ; posterior margin regularly rounded ; 

 base straight, and parallel to the cardinal margin in the middle, 

 and rounding up to the anterior and posterior margins; anterior 

 side short, rounded or somewhat truncated, but apparently most 

 prominent below ; hinge line shorter than the valves, straight 

 behind the beaks, but rounding into the posterior margin at the 

 extremit}^, erect behind, with some appearance of a narrow space 

 for an external ligament farther forward ; beaks about one-fourth 

 the length of the valves from the anterior margin, raised a little 

 above the cardinal margin, nearly contiguous, but not much in- 

 curved. Surface of a cast, that seems to be a little weathered or 

 smoothed by attrition, showing obscure marks of growth. 



Length, 0.77 inch; height, 0.59 inch; convexity, 0.29 inch. . 



I have only seen a single specimen of this species ; and, as it is 

 a mere cast, not showing clearly even the surface markings, little 

 can be said in regard to its affinities. I am even left in some 

 doubts whether its shorter side may not be the posterior instead 

 of the anterior, as there is some appearance about the points of 

 the beaks of their being rather directed toward the longer than 

 toward the shorter side. The appearance, however, of a narrow 

 space along the cardinal margin on the longer side, as if for an 

 external ligament, seems to indicate that this is the posterior. 

 The margins of the valves on the anterior? (shorter) side are a 

 little defective above in the specimen, so as to leave room for 

 some doubts whether it was regularly rounded in outline or not. 



Although the specimens of the last-described species are much 

 distorted, it is evident, I think, that they are quite distinct from 

 this, as it would seem impossible to make this shell assume the 

 shape and convexit}'- of the last by any conceivable degree of 

 distortion. 



Mr. James referred this species, in his list, to the Upper Silu- 

 rian form Anatinaf simiata, Hall, which it resembles in form- 

 Still, it seems to me to differ too much in its more elevated beaks, 



[February 13, 



