Lamellibranchiata. 279 



produced behind and extending thence in nearly a direct line* to the 

 beak. Left valve depressed-convex. Right valve not known. 

 Hinge-line straight, anterior, less than half the length of the shell. 

 Beak obtuse, rounded, low, inclined a little forward. Umbonal 

 region scarcely denned, subtending about a right angle. Ears 

 nearly equal ; margins concave. The posterior ear extends along 

 the posterior margin as a narrow expansion. In well-preserved 

 specimens the ears are defined by sulci. Byssal sinus inconspicu- 

 ous. 



Obscure evidences of concentric striae appear in the casts. In- 

 ternal characters unknown. 



Two specimens have respectively the following dimensions : length 

 24 and 16 mm., width 26 and 19 mm., hinge-line 9 and 7 mm. 



In general form and convexity this species resembles C. crenulatus, 

 but it is narrower above, with the hinge-line comparatively much 

 shorter. 



The specimens are casts of the interior preserved in coarse sand- 

 stone ; the surface markings are consequently obliterated. 



Formation and locality, In a coarse sandstone of the Chemung 

 group near Olean, Alleghany county, N. Y. 



Creihpecteh obsoletus. 



Lima? dbsoleia, Hall. Geolog. Surv. N. Y.; Rep. Fourth Dist.,p. 265. 1843. 

 Crenipecten obsoletus, Hall. Pal. N.Y., vol. v, pt. 1. Plates and Explanations : 

 PI. 9, figs. 19, 21. Jan., 1883. 



Shell small, obliquely sub-ovate; length nearly equal to the height ; 

 margins regularly curved, becoming produced on the post-basal side, 

 and somewhat rectilinear on the posterior side. Valves very similar. 

 Eight valve depressed-convex. Left valve regularly convex. Hinge- 

 line straight, a little more than one-half the length of the shell. 

 Beak obtuse, more prominent on the left valve ; situated in the 

 center of the hinge. Umbonal region well-defined in the left valve ; 

 depressed and undefined in the right valve. Ears small, triangular, 

 sub-equal, defined by shallow sulci ; margins gently concave ; ex- 

 tremities obtuse. Posterior ear a little the larger. Byssal sinus not 

 conspicuous. 



Test thin, marked by fine, closely arranged, concentric striae, 

 which are crowded and stronger on the ears. No radiating striae 

 have been discovered. Ligamental area narrow, marked by a row 

 of minute cartilage-pits. 



A left valve measures 18 mm. in length, 20 mm. in height, hinge- 



