264 Thirty-fifth Keport on the State Museum. 



margin very sjightly concave ; extremity rectangular. Anterior ear 

 smaller, not distinctly denned from the body of the shell; margin 

 above the sinus convex ; extremity acute. Byssal sinus moderate. 



Entire surface marked by distinct, close, rounded, duplicating 

 radii, crossed by fine, concentric lines of growth. The surface of 

 the umbonal region is wrinkled from the apex to below the middle 

 of the valve. The surface markings are finer and sub-equal over 

 the posterior ear. A small space on the umbo, as in Aviculopecten 

 lellus, is destitute of radii. 



This species differs from P. Hermes in its less oblique form, shorter 

 hinge-line, less ample umbo, and in having no regular alternation in 

 the rays, which are closer and more rounded. It is associated with, 

 and closely allied to P. dignatus, but differs by its more obtuse beak, 

 longer outline, and comparatively more frequent and smaller rays, 

 without the regular concentric striae. 



Formation and locality* In the Marcellus shale at Bloomfield, 

 Ontario county, N. Y. 



Pterinopecten Hermes. 



Pterinopecten Hermes, Hall. Pal. 1ST. Y., vol. v, pt. I. Plates and Explanations : 

 PI. 17, figs. 13-15. Jan., 1883. 



Shell less than medium size, sub-rhomboidal, obliquely sub-ovate; 

 length and height about as three to four ; pallial margins regularly 

 rounded, becoming straight on the post-cardinal slope at the junction 

 with the ear. Left valve moderately convex. Eight valve not de- 

 termined. Beak acute, prominent, anterior to the middle of the 

 shell, directed forward. Umbonal region ample, subtending an 

 angle of about 80°. Ears very unequal, triangular. Posterior ear 

 much the larger, scarcely defined ; margin concave ; extremity acute. 

 Anterior ear small, slightly convex, defined by a distinct sulcus ; 

 margin convex ; extremity rounded. Byssal sinus deep. 



Test marked by regular, rounded striae, with wider interspaces 

 which, on the posterior part of the valve, show finer intermediate 

 rays. The ears have essentially the same surface characters as the 

 body of the valve. The entire surface is marked by fine concentric 

 striae. Umbo with concentric wrinkles. Partial casts of the interior 

 show the same characters as the exterior, but show no muscular or 

 pallial markings. 



The largest specimen observed has a length of 19 mm., height 29 

 mm., hinge-line 29 mm. 



