228 PALEONTOLOGY OF THE EUREKA DISTRICT. 
Surface marked by from 25 to 30 simple radiating cost, the inter- 
spaces wider than the cost, and with intercalated smaller cost rising in 
some of them; concentric strize and lines of growth are more or less dis- 
tinctly shown. Right valve unknown. 
The interior of the hinge unknown. 
Dimensions: height and width of average size specimen, 3.5™; con- 
vexity of left valve, .75°™. 
This species shows considerable similarity to A. Eurekensis. It differs 
in the presence of a larger number of costz and in its more orbicular form. 
Formation and locality—Lower portion of Lower Carboniferous lime- 
stone in canon directly south of a conical hill on east side of Secret-cafion- 
road Canon, Eureka District, Nevada. 
Aviculopecten Pintdensis, n. sp. 
Plate viii, fig. 6. 
Shell small, rounded ovate in outline exclusive of the wings. Left 
valve gently convex. Hinge-line about two-thirds as long as the greatest. 
width of the shell below. Ears subequal in size, the anterior with a some- 
what more deeply cut, rounded sinus beneath. Beak small, obtusely 
pointed and scarcely extending beyond the cardinal margin. 
Surface marked by numerous fine radiating linear cost, twenty in 
a distance of five millimeters, with a few finer strize or coste in some of the 
interspaces; the coste are present on the ears and are strongly defined on 
the anterior ear; a few concentric lines of growth appear on the posterior 
ear and extend on to the disk of the shell as rather indefinite undulations 
or lines of growth. 
Interior characters unknown. 
Dimensions: height, 2; width, 2°; convexity of left valve, 2™. 
This pretty little shell is of the type of Aviculopecten Coxanus M. and 
W. (Geol. Surv. Ill, vol. ii, plate xxvi, fig. 6a, b), differing only in its more 
erect form and shorter ears. In form it also approaches A, (Pecten) plicatus 
Sowerby, as figured by De Koninck (Anm. Foss., plate iv, fig. 6). 
Formation and locality—Lower portion of Carboniferous Group, in 
canon north of Pinto Peak, Eureka District, Nevada. 
