Lamellibranchiata. 239 



AVICULOPECTEN" (PTERINOPECTEN ?) INTALIDUS. 



Pterinopecten invalidus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explana- 

 tions: PI. 1, fig. 18. Jan., 1883. 



Shell small, rhomboidal; length and height nearly equal; moderately 

 oblique ; margins regularly rounded, full behind ; the greatest pos- 

 terior extension is below the middle. Left valve depressed-convex. 

 Eight valve unknown. Hinge-line nearly straight, length a little 

 more than the length of the valve, and extending anteriorly. Beak 

 obtuse, rounded, situated just anterior to the center of the hinge- 

 line, directed slightly forward, depressed. Umbonal region moder- 

 ately prominent, subtending an angle a little less than 90°. Ears 

 triangular, flat, extremities acute. Anterior ear smaller, defined by 

 a sulcus; margin nearly straight. Posterior ear with the margin 

 concave, extremity acuminate ; having no strong radiating striae. 



Test, as indicated in an exfoliated specimen, marked by a few fine 

 radiating striae, with wider interspaces which are marked by finer 

 radii. Anterior ear showing the same characters. Posterior ear free 

 from rays. Fine concentric striae cross the rays, and stronger con- 

 centric wrinkles interrupt them and produce a slight crenulation of 

 the radii. 



The specimen is 10.5 mm. in length, 10 mm. in height, with 

 hinge-line a little more than 11 mm. 



This species resembles in form the young of Pterinopecten dignatus, 

 but differs in the finer radiating lines on the body of the shell, the 

 concave margin, and absence of rays on the posterior ear. 



Formation and locality . In the black Marcellus shale at Cherry 

 Valley, Otsego county, N. Y. 



AviCULOPECTEN (PTERINOPECTEN ?) TERMINALIS. 



Pterinopecten terminates, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explana- 

 tions : PI. 1, fig. 3. Jan., 1883. 



Shell small, rhomboidal ; body of the shell obliquely ovate ; length 

 a little greater than the height ; margins regularly rounded, some- 

 what extended behind. Left valve very convex. Right valve un- 



". known. Hinge-line straight, central, equal to the length of the 

 shell. Beak acute, prominent, directed a little forward, arching over 

 the hinge-line. Umbo elevated, subtending a right angle. Ears 

 triangular ; margins concave ; extremities acute. Posterior ear 

 larger, undefined. Anterior ear limited by a shallow sulcus. Byssal 

 sinus moderate. 



