FOSSILS OF THE DEVONIAN. 127 
is so great that the two extremes will readily be taken as distinct species, 
to avoid which an illustration is given of the younger and older shells with 
an intermediate form. The outer surface of the ventral valve of the shell 
is exfoliated, the characteristic striz showing on the dorsal valve of the 
same specimens 
Formation and localities—Lower horizon of the Devonian limestone, 
Comb’s Peak; ‘south spur of Atrypa Peak; ‘on the divide of the Reese and 
Berry Cafion, and midway of Gray’s Canon, Eureka District, Nevada; also 
at the same horizon at the north end of the Ravens Nest, Pinon Range, 
Nevada. 
Chonetes filistriata, n. sp. 
Plate xiii, figs. 15, 15a. 
Shell transverse, broadly subelliptical, varying in proportion from 4 to 
8, to 3 to 2, in breadth and length, respectively; the hinge-line is a trifle 
shorter than the greatest width of the shell, and the cardinal angles are ex- 
tended in very short auriculate points. 
Ventral valve moderately convex, the convexity varying but slightly 
between the young and old shells; the outline of the valve is regularly 
convex, rising from the cardinal margin and sloping more rapidly from the 
broad central portion towards the front and lateral margins; cardinal margin 
with three or more short, slightly oblique spines on each side of the apex. 
The area is narrow, linear, and divided midway by a rather broad triangular 
foramen that is nearly filled by the cardinal process of the opposite valve. 
The dorsal valve is moderately concave, following very nearly the 
curvature of the ventral valve. Area linear and very narrow. 
Surface marked by numerous fine, closely arranged striz, that increase 
by intercalation and bifurcation; they extend to nearly the hinge line on 
the cardinal extremities, and vary in number from 80 to 90 on the lower 
portion of a medium-sized shell. A few specimens show faint undulating 
concentric striz. 
The specimens are all preserved in a shaly limestone and the interiors 
of the valves have not been observed. 
Numerous shells corresponding in general form and size with this spe- 
