FOSSILS OF THE CARBONIFEROUS. 



227 



Dimensions : height, 9.5 cm ; width, 8 cm ; convexity of left valve, 1.25 cm . 



This is an unusually large and strongly marked species, and unlike any 

 described from this horizon. 



Formation and locality. Lower portion of the Carboniferous Group, 

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

 hill, Eureka District, Nevada. 



Aviculopecten Eurekensis, n. sp. 

 Plate xix, figs. 2, 3. 



General outline exclusive of the ears subovate, varying somewhat in 

 different specimens. General surface moderately convex when not acci- 

 dentally compressed; ears subequal in size, the posterior being the larger, the 

 anterior shorter and more obtuse. Hinge-line less than the greatest width 

 of the shell. Beak small, obtusely pointed. 



Surface marked by from 18 to 25 simple lines or radiating costse, that 

 are crossed by fine concentric striae. Left valve unknown. The hinge is 

 smooth each side of the beak. 



Dimensions : height of narrow form, 4 cm ; of broad form, 3.5 cm ; width, 

 3.5 cm and 4 cm ; convexity of left valves, l cm and 0.75 cm , respectively. 



This species is allied to A. Haguei, but differs in having about one-half 

 the number of radiating surface costre. 



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

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

 Canon, Eureka District, Nevada. 



Aviculopecten peroccidens, n. sp. 



Plate viii, fig. 8. 



General outline, exclusive of the ears, suborbicular to subovate in the 

 more elongate specimens. General surface rather strongly convex when 

 not flattened by accidental compression. Anterior ear considerably smaller 

 than the posterior. Hinge-line less than the greatest width of the shell 

 below. Beak subcentral. Angle of divergence of the body of the shell 

 from the beak, within the ears, 110. 



