FOSSILS OF THE CABBONIFEKOUS. 



233 



In outline this species* is not dissimilar from Pterinopecten (Pecten) 

 papyraceus, as illustrated by De Koninck (Anm. Foss., plate v, figs. 6, 6 a, 6). 

 It differs widely in surface characters. I know of no American species 

 with which to compare it. 



Formation and locality. Lower portion of the Carboniferous Group, on 

 the east slope of a small conical hill on the east side of Secret-canon-road 

 Canon, Eureka District, Nevada. 



Pterinopecten Spio, n. sp. 

 Plate viii, figs. 1, 1 a. 



Outline, including the ears, broadly truncato-ovate. Left valve de- 

 pressed convex. Hinge-line nearly as long as the greatest width of the 

 shell below. Anterior ear small, separated more sharply from the body 

 of the shell than is usual in the genus; sinus rounded; posterior ear large 

 and not very distinctly separated from the body of the shell. Beak small, 

 abruptly pointed, and situated nearly on the anterior third of the length of 

 the hinge-line. 



Surface marked by about 20 linear, radiating costae, with inter-spaces 

 greater than the width of the costse, in which faintly-defined costae are 

 sometimes shown ; concentric lines of growth occur, and under peculiar 

 conditions of preservation, as shown in fig. 1 of plate viii, form a reticu- 

 lated structure with the radiating costae. 



Dimensions : height of an average specimen, 15 mm ; width, 18 mm ; con- 

 vexity of left valve, 2 mm to 3 mm . 



In outline and the form of the wings this species approaches that of 

 Pterinopecten exfoliatus Hall, of the Devonian of New York (Pal. N. Y., vol. 

 v, pt. 1, p. 61, 1884), more nearly than to any other species known to me. 



Formation and locality. Lower portion of Lower Carboniferous lime- 

 stone in canon directly south of a small conical hill on east side of Secret- 

 canon-road Canon, Eureka District, Nevada. 



