LAMELLIBRANCHIA TA. 
81 
The comparison with P. crenicostatus is given under the description of that 
species. It resembles the young of Lyriopeden orbiculatus, but the details of the 
characters are quite different. 
Formation and localities. In the Chemung group at Hobbieville and Elm 
Yalley, Alleghany county; New Albion, Cattaraugus county, N. Y., and 
Mansfield, Tioga county, Pennsylvania. 
CRENIPECTEN* Hall. 
Ckenipecten amplus. 
PLATE IX, PIGS. 9, 13, 18. 
Crenipecten amplus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 9, figs. 9,13. Jan., 1883. 
Creni.pecten crenulatus ? Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 9, fig. 18. Jan., 1883. 
Shell larger than medium, broadly and obliquely ovate; height about one- 
sixth greater than the length; margins regularly rounded, more extended 
posteriorly. 
Left valve very convex. Right valve not known. 
Hinge-line straight, about equal to one-half the length of the shell, situated 
a little anterior to the middle. 
Beak obtuse, erect, prominent. Umbonal region very convex, well 
defined, subtending a right angle. 
Ears nearly equal; margins gently concave. Posterior ear somewhat the 
larger, defined by a sulcus. Anterior ear defined by a sulcus which is more 
distinct and abrupt. Byssal sinus shallow. 
Surface of the cast marked by fine, irregular, concentric striae, with 
obsolescent, fine radiating lines. Ligamental area narrow and distinctly 
crenulate. 
* Tlie forms here described under this generic term have in part been referred to Pernopecten by Pro¬ 
fessor Winchell; but a critical study of the type species of that genus shows that it possesses a large central 
cartilage-pit with a crenulated hinge-plate on each side below the hinge-margin, which characters alone are 
sufficient to distinguish the genus and exclude the forms here described under Crenipecten. See discus¬ 
sion of the relations of Pernofecten, Entolium and Crenipecten, in the introduction to this volume. 
11 
