260 Thirty-fifth Report on the State Museum. 



pressed-convex ; margin reflexed. Right valve unknown. Hinge- 

 line straight, extended posteriorly, exceeding the greatest length of 

 the shell. Beak obtuse, low, rounded, directed forward. Umbonal 

 region convex, subtending an obtuse angle. Posterior ear large, 

 flat, triangular, scarcely defined from the umbo ; margin slightly 

 convex ; extremity obtuse. Anterior ear small, triangular, convex? 

 limited by an undefined sulcus and a shallow byssal sinus ; margin 

 nearly straight ; extremity obtuse. 



Test marked by fine rounded striae, alternating with finer lines ; 

 intermediate spaces flat. The same surface marking continues in a 

 subdued degree upon the posterior ear, and somewhat more strongly 

 on the anterior slope and anterior ear. 



The specimen figured has a length, across the middle, of 18 mm., 

 height 15 mm., hinge-line 22.5 mm. 



In form, this species resembles P. Hermes, but is distinct in its 

 smaller and less defined anterior ear, less strong radii, and more de- 

 pressed beak. It is much flatter and of different proportions from P. 

 exfoliatus. 



Formation and locality. In the Oorniferous limestone at the falls 

 of the Ohio, near Louisville, Ky. 



Pterinopectek insons. 



Pterinopecten fnsons, Hall. Pal. N.Y., vol. v, pt. 1. Plates and Explanations ; 

 PI. 1. fig. 4. Jan., 1883. 



Shell small, rhomboidal, slightly oblique ; length somewhat greater 

 than the height ; basal margin regularly rounded ; the anterior and 

 posterior sides become nearly vertical as they approach the ears. 

 Left valve convex, the greatest convexity near the beak. Right 

 valve unknown. Hinge-line straight, length one-fourth greater 

 than the length of the shell, extended posteriorly. Beak acute, 

 prominent, anterior to the middle of the hinge, directed forward. 

 Umbonal region prominent, subtending a right angle. Ears trian- 

 gular ; margins straight ; extremities acute. Posterior ear large, 

 undefined. Anterior ear small, convex, with an undefined fold 

 below the cardinal margin, limited by a distinct rounded sulcus. 

 Byssal sinus slightly marked. 



Test (in a partially exfoliated specimen) marked by regular, sharp, 

 not numerous rays, with broad, flat interspaces, which, in a perfect 

 condition, have probably been marked by fine striae. The rays are 

 obsolete over the posterior slope of the valve and the umbo, and 



