232 PALEONTOLOGY OF THE EUEEKA DISTRICT. 



than the posterior, and also with an abruptly curved sinus beneath it. Beaks 

 small and abruptly pointed, subcentral in position on the hinge-line. 



Surface of both right and left valves marked by linear, radiating, raised 

 striae that increase in number towards the margin by the striae originating 

 in the gradually widening interspaces between the initial striae, the striae at 

 the basal margin being about l mm apart. Fine concentric striae cross the 

 radiating elevated striae or costae. 



The left valve of this species is closely allied to that of Crenipectm 

 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 liganiental 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 cafion north of Pinto Peak, and also on the east slope of a 

 small conical hill on the east side of Secret-canon-road Cafion, Eureka 

 District, Nevada. 



N 



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 striae that increase in number by intercalation as the initial striae 

 spread apart, the intercalated striae appearing between them. 



Dimensions: height, 4.5 cm ; breadth, 4.75 cm . 



