410 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Pedicle valve nearly plane or gently concave in lateral profile. Fold low and 
narrowly rounded, originating on the umbo and extending anteriorly for about 
two-thirds to three-fourths the length where it disappears in a short and shallow 
sulcus that depresses the front of the valve. Lateral areas nearly flat. Interarea 
short and apsacline. 
Brachial valve evenly and moderately convex in lateral profile; slightly more 
convex but broader in anterior profile. Sulcus not deeply impressed and extend- 
ing to about the middle or anterior third. Entire valve gently inflated and with 
long moderately steep slopes to the anterior and lateral margins. 
Pedicle interior with the usual muscle area having elongate diductor impres- 
sions but a fairly wide and large adductor track. Pallial marks occasionally 
deeply impressed. Median ridges inside brachial valve strong, fairly elevated, 
and extending slightly anterior to the middle. 
Measurements in mm.— 
Hinge 
Length Width width Thickness 
TIQIOEU DEY sis dict c Powis aia a! ae xieioin,  wteimretelereeets 12.4 19.7 ? 2.9 
Paratype (pedicle valve 116968b)....... 9.0 15.5 20.6 ? 
" (brachial valve 116968a)...... 10.0 17.9 22.4 ty 
Types.—Holotype: 116967; figured paratypes: 110265a,c; 116968a,b, 
117994a; unfigured paratypes: 110265b,d-f, 116969, 117994b-g. 
Horizon and locality—Yellow limestone overlying 25-foot sandstone at base 
of Eureka group, Roberts Mountains (1°) Quadrangle in Nevada: 2 to 3 miles 
north of Martin Ranch; on crest of Antelope Range, 3 miles south of Nine Mile 
Canyon; saddle just north of hill 8167, Martin Ridge, Monitor Range. 
Discussion.—No other species is quite like this one in having such a flat pedicle 
valve. This character is approximated by V. austrina, but that is a larger species 
than the Nevada one and differently ornamented. Valcourea plana occurs with 
abundant specimens of Sowerbyites, which help to fix its age as about that of 
the Lincolnshire formation of Viriginia and Tennessee and the basal part of the 
Bromide in Oklahoma. 
VALCOUREA SEMICARINATA Cooper, new species 
Plate 70, A, figures 1-10 
Valcourea strophomenoides Butts, Virginia Geol. Surv. Bull. 52, pt. 2, p. 41, pl. 73, figs. 9, 10, 
1942, 
Shell of about medium size for the genus, wider than long with the hinge 
usually forming the widest part ; cardinal extremities varying from alate to nearly 
a right angle. Lateral margins oblique, anterior margin broadly rounded. Sur- 
face multicostellate, costellae about 3 or 4 to the millimeter at the front margin. 
Pedicle valve gently convex in lateral profile in the posterior half but gently 
to moderately convex in the anterior half. Umbo carinate, the carina low and 
extending to about the center where it is lost in a broad shallow depression or 
continued to the front margin as a broader but very faint undulation. Areas 
bounding carina gently concave but the posterolateral areas flattened and bent 
