62 
PALAEONTOLOGY OF NEW YORK. 
extended posterior ear. It is more gibbous and less oblique than P. Hermes, 
with less conspicuous striae. 
The specimens are usually in the condition of partially exfoliated casts, and 
retain marks of only the stronger radii and concentric undulations. The 
differences between the internal mould and the impression of the exterior 
of the shell are represented in figs. 6, 7, of pi. lxxxiii. 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. 
Pteeinopecten dignatus. 
PLATE I, FIGS 12, 14, 15. 
Pterinopecten dignatus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 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. Right valve depressed, flatter and smaller 
than the left; it differs 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; deep, narrow and angular in the right valve. 
Test of the left valve marked by numerous strong, rounded, increasing 
radii, with broader interspaces, containing one or two smaller rays which 
originate about the middle of the valve; crossed by fine, sharply elevated, 
concentric striae. The right valve is marked by fine, sub-equal, regular, 
