236 PALEONTOLOGY OF THE EUREKA DISTRICT. 
This species is allied to Pinna Missouriensis Swallow (Trans. St. Louis 
Acad. Sci., vol. ii, p. 97, 1863), but from the description of that species it 
appears to differ in form and surface markings. It differs from P. flexicostata 
McCoy (Brit. Pal. Foss., p. 499), in being more elongate, and also in hay- 
ing the radiating plications on the entire lower half of the valves. 
Formation and locality.—Lower portion of the Carboniferous Group, on 
east slope of a small conical hill on the east side of Secret-canon-road Canon, 
Eureka District, Nevada. 
Pinna consimilis, n. sp. 
Plate xx, fig. 13. 
Valves elongate, about three and one-half times longer than the width 
at the posterior end; the upper and lower margins converging at an 
angle of 20° towards the beaks, where the shell is pointed and subcylin- 
drical, the section becoming more and more elliptical toward the posterior 
end, which is slightly and obliquely rounded ; cardinal margin a little thick- 
ened and with a narrow, well-defined, rounded rim or cardinal ridge. 
Surface marked by concentric lines of growth; otherwise smooth. 
The description is drawn from a small specimen 11° in length, but 
fragments of individuals of twice the size were found. The species is allied 
to P. spatula McCoy (Brit. Pal. Foss., p. 499), but differs in being less elon- 
gate in proportion to the width, the outline being more that of the plicated 
species, P. flewicostata McCoy (loc. cit., p. 499). I know of no closely related 
American species, P. subspatulata Worthen (Geol. Surv. Ill, vol. vi, p. 524), 
being a much more elongated form. 
Formation and localities—Lower portion of the Carboniferous with the 
preceding species, and also on the northeast side of the cation north of Pinto 
Peak, Eureka District, Nevada. Also at about the same horizon on the 
west slope of Mokomoke Ridge, White Pine District, Nevada. 
