LAMELLIBRANCHIATA. 67 



left valve ; deep and angular in the right valve, as ween in the specimen 

 figured. 



Test of the left valve marked by comparatively few, strong, rounded radii, 

 with intermediate smaller ones, crossed by fine concentric striae of growth, 

 and strong undulations which interrupt the continuity of the radii. Right 

 valve marked by numerous sub-equal radiating stri* which are somewhat 

 obsolete near the beak, and the umbonal region is marked by some strong 

 concentric wrinkles. Tlie ears present, in a less degree, the same ornamen- 

 tation as the body of the shell. 



Internal characters not observed. Ligameutal area simple. 



A mature specimen is 27 mm. in length and height, and the hinge-line 

 28 mm. 



This species differs from P. dignatm in being less oblique, the anterior ear 

 less extended, and the radii sharper and more interrupted. It differs from 

 P. latus and P. Hermes in the less obliquity and the stronger surface markings. 

 It differs from P. invalidus, which is similar in general aspect, in being wider, 

 and the margin of the posterior ear less concave. 



Formation and localities. In the Hamilton group at Norton's Landing, Cayuga 

 lake, and shores of Skaneateles lake, N. Y. 



Pterinopecten filitextus. 



PLATE XVn, FIG. Si ; AND PLATE LXXXII, FIGS. 9, 10. 



Pterinopecten filitextus. Hall. Pal. N. V., v<il. v, pt. 1. Plates and Explanatioiis : PI. l". fig-. 22. 



Jan., IS83. 



Shell larger than medium size, transversely semi-elliptical, scarcely oblique ; 

 length somewhat greater than the height ; margins regularly rounded, less 

 convex on the posterior side. 



Left valve moderately convex. Right valve flat or concave. 



Hinge-line straight, about as long as the length of the shell, not extended 

 anteriorly beyond the margin. 



