232 PALEONTOLOGY OF THE EUREKA DISTRICT. 
than the posterior, and also with an abruptly curved sinus beneathit. Beaks 
small and abruptly pointed, subcentral in position on the hinge-line. 
Surface of both right and left valves marked by linear, radiating, raised 
strize that increase in number towards the margin by the striz originating 
in the gradually widening interspaces between the initial striae, the strize at 
the basal margin being about 1™” apart. Fine concentric striz cross the 
radiating elevated strize or coste. 
The left valve of this species is closely allied to that of Crenipecten 
Winchelli (see Pal. N. Y., vol. v., pt. 1, p. 89), except in being more robust. 
In the right valve marked differences occur in the surface characters and 
the shape of the anterior ear. With Aviculopecten affinis it is more closely 
related, differing mainly in the form and proportion of the ears, in its more 
robust form, and the presence of the ligamental pits on the hinge-line, 
which, as yet, have not been observed in the latter, although the conditions 
for their preservation and discovery appear to be much better than in C. 
Hallanus. 
Formation and localities —Lower portion of the Lower Carboniferous 
Group in the cation north of Pinto Peak, and also on the east slope of a 
small conical hill on the east side of Secret-canon-road Cation, Eureka 
District, Nevada. 
Genus PTERINOPECTEN Hall. 
Pterinopecten Hoosacensis, n. sp. 
Plate viii, fig. 9. 
Outline truncato-ovate. Left valve depressed convex. Hinge-line 
nearly as long as the greatest width of the shell below. Anterior ear de- 
fined by a strong rounded sinus; posterior ear scarcely more than a slight 
extension of the postero-lateral portion of the shell. Beak small, abruptly 
pointed, and situated a little anterior to the center of the hinge-line. 
Surface marked by a few concentric lines of growth and fine, linear, 
raised striz that increase in number by intercalation as the initial striz 
spread apart, the intercalated striz appearing between them. 
Dimensions: height, 4.5°™; breadth, 4.75. 
