LAMELLIBRANCHIA TA. 
71 
fig. 22 of pi. 17, is imperfect at the posterior extremity of the hinge, and 
thus resembles the present form more than it would if properly restored. 
Formation and localities. In the shales of the Hamilton group, between 
Geneseo and Avon, and at Delphi, N. Y. 
Pterinopecten Verttjmnus. 
PLATE V, FIGS. 1-8 ; and PLATE LXXXIII, FIGS. 2, 3. 
Pterinopecten Vertumnus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PL 5, figs. 1-8. 
Jan.. 1883. ' 
Shell large, rhomboidal, oblique; greatest length below the middle of the valve ; 
length about one-fifth greater than the height; margins regularly rounded, 
becoming full behind and sloping rapidly to the hinge-line. 
Left valve depressed-convex. Right valve nearly flat. 
Hinge-line straight, somewhat shorter than the length of the shell. 
Beaks obtuse, low, anterior to the middle of the hinge-line, directed 
forward. Umbonal region moderately convex in the left valve, depressed 
in the right valve, limits defined anteriorly, but not posteriorly. 
Ears triangular, flat. Posterior ear much the larger, not defined from 
the body of the valve ; margin gently concave; extremity acute. Anterior 
ear small, separated from the umbo by an undefined sulcus, and in the right 
valve by the marked, angular byssal sinus; margin concave; extremity acute, 
sometimes rounded. 
Surface of left valve marked by irregularly alternating, strong, flexuous, 
flattened radii; interspaces flat; crossed by sharp, elevated, concentric stria3 
which are more closely arranged towards the margin of the shell. The 
same character of surface continues over the ears, and on the posterior ear 
the radii are finer, nearly equal in strength, and crenulated by the concen¬ 
tric striae. On the right valve the rays are more equal and finer than on the 
opposite valve; conspicuous on the posterior ears and subdued on the 
anterior. 
Three specimens have respectively the following dimensions: length 
38, 40, 41 mm., height 30, 33, 29 mm., hinge-line 35, 35, 32 mm. 
