62 PALEONTOLOGY OF NEW YORK. 



(.■xti-mli'il posti'iior oiir. It is iiiore' ^ibhous and l(j.s.s oblique than P. Hermes, 

 with less conspicuous stria\ 



The specimens are usually in tlie condition of partially exfoliated casts, and 

 retain marks of only the stronger radii ami concentric undulations. The 

 diflerences Ix'twei ii tlic internal mould and the impression of the exterior 

 of the shell are represented in figs. 6, 7, ^A' pi. Ixxxiii. This species is not 

 uncommon in the central and western portions of the State. 



Formation and hcalities. Tn a limestone bed of the Marcellus shale at Avon, 

 Livingston county, Staflord, (Jenesee county, and A^ienna, Ontario county, 

 N. Y. 



Pterixopecten dignatus. 



I'l.ATE I, FIGS 12, 14, Ifi. 



Pterinopecten diffnatiis. Hall. Pal. N. Y., vol. v, pt. 1. Platos and Explanations: PI. 1, fijrs. 12. 14, 1.5. 



Jan., 1883. 



SiiEi.i, small, sub-rhomlM)idal, 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. Right valve depressed, flatter and smaller 

 than the left : it diiVi'is in surface markings and depth of byssal notch, and 

 is apparently thinner and more delicate. 



Hinge-line straight, length equalling, or greater than, the greatest length 

 of the shell, extending anteriorly beyond the margin of the valve. 



Beaks obtuse, rounded, anterior to the centre of the hinge-line, directed 

 slightly forward. Umbonal region ample, subtending an acute angle. 



Ears triangular, flat. The posterior ear larger and less distinctly defined 

 than the anterior ; margin straight or .slightly concave; extremity rectangular. 

 Anterior ear rounded ; margin convex ; extremity acute-angular. Byssal sinus 

 moderate in the left valve; dee]!, ii.in-ow and angular in the right valve. 



Test of the left \alve marked In numerous strong, rounded, increasing 

 radii, witli l)roader interspaces, containing one or two smaller rays which 

 originate about the middle of the valve; crossed l)y fine, sharply elevated, 

 concentric striie. The right valve is marked l)y fnie, sub-eciual, regular. 



