262 Thirty-fifth Report ok the State Museum. 



tremitjof the hinge. Left valve very convex, inclined to gibbosity. 

 Right valve moderately convex, much smaller than the left. Hinge- 

 line straight, a little longer than the greatest length of the shell, ex- 

 tended posteriorly. Beak of left valve prominent, sub-acute, 

 anterior to the middle of, and arching over the hinge-line, directed 

 forward. Umbo prominent, gibbous, the greatest convexity being 

 about the middle of the width subtending a right angle. Ears 

 triangular. Posterior ear large, undefined; margin slightly con- 

 cave ; extremity somewhat acute. Anterior ear small, convex, 

 defined by a deep, obtuse sulcus ; margin convex ; extremity acutely 

 rounded. Byssal sinus distinct, somewhat deep. 



Test thin, marked in the left valve by fine, regular, radiating 

 strise with flat interspaces which show one or two finer rays; 

 crossed by concentric lines of growth and stronger undulations, 

 which in old shells become very prominent. The rays are continued 

 over the ears, and are somewhat subdued and less distinctly alternat- 

 ing on the posterior ears, and obsolete over the upper part of the 

 umbo. The right valve is marked by obsolescent rays and concen- 

 tric undulations. Ligamental area narrow. 



Three specimens measure respectively as follows : length, 17, 20 

 and 22 mm., height, 15, 18 and 18 mm., length of hinge-line, 18, 

 21 and 23 mm. 



In the exfoliated condition, this species resembles P. insons; but 

 has a comparatively shorter hinge-line, smaller anterior ear, deeper 

 byssal sinus, and less extended posterior ear. It is more gibbous and 

 less oblique than P. Hermes, with less conspicuous striae. The speci- 

 mens are usually in the condition of partially exfoliated casts, and 

 retain marks of only the stronger radii and concentric undulations. 

 This species is not uncommon in the central and western portions of 

 the State. 



Formation and localities. In a limestone bed of the Marcellus shale 

 at Avon, Livingston county, Stafford, Genesee county, and Vienna, 

 Ontario county, N. Y. 



Pterinopecten" dignatus. 



Ptevinopecten dignatus, Hall. Pal. N.Y., vol. v, pt. 1. Plates and Explana- 

 * tions : PI. 1, figs. 12, 14, 15. Jan., 1883. 



Shell small, sub-rhomboidal, very slightly oblique ; length and height 

 as three to four ; pallial margins regularly rounded, somewhat more 

 produced on the postero-lateral portion. Left valve moderately 

 convex. Eight valve depressed, flatter and smaller than the left ; 



