FOSSILS OF THE CARBONIFEROUS. 221 
Dimensions : height, 9.5™; width, 8°"; convexity of left valve, 1.25°™. 
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 Canon, 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 costz, that 
are crossed by fine concentric strie. Left valve unknown. The hinge is 
smooth each side of the beak. 
Dimensions : height of narrow form, 4°; of broad form, 3.5™; width, 
3.5°™ and 4°™; convexity of left valves, 1™ and 0.75™, respectively. 
This species is allied to A. Haguei, but differs in having about one-half 
the number of radiating surface costae. 
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°. 
