LAMELLIBRANCHIA TA. 
75 
of the posterior ears, do not assimilate it with the ordinary characters ascribed 
to those genera. 
Formation and locality. In the Chemung group near Elmira, N. Y. 
Pterinopecten imbecilis. 
PLATE XXIV, FIG. 1. 
Pterinopecten imbecilis. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PL 24, tig. 1. 
Jan., 1883. 
Shell small, rhomboidal, oblique, much longer than high; anterior and basal 
margins rounded; posterior margin produced. 
Left valve moderately convex. Right valve not known. 
Hinge-line equal to, or greater than, the length of the body of the shell. 
Beak obtuse, directed forward, rather prominent. Umbonal region ample, 
defined anteriorly ; subtending an angle of about 90°. 
Ears very unequal, triangular. Anterior ear small, defined by a distinct 
sulcus. Posterior ear large, undefined; margin concave; extremity angular. 
Surface marked by numerous strong, simple radii, with wider interspaces 
which have usually finer intermediate radii; crossed by fine, equal concentric 
lines of growth, and stronger, more distant lamellae, which are elevated and 
arched backwards over the larger rays, producing nodes. 
Internal characters not preserved. 
The specimen has a length of 15 mm., height 11 mm., hinge-line about 
15 mm. 
This species differs from P. Imtus, by its distinct and widely separated rays, 
and more oblique outline. 
Formation and locality. In the Chemung group at Tioga, Tioga county, Penn¬ 
sylvania. 
