340 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
quartzite) in Nevada: At the base of first ridge east of Frenchman Flat, Las 
Vegas (1°) Quadrangle; at the Narrows 2 miles up Whiterock Canyon, Roberts 
Mountains (1°) Quadrangle. 
ORTHIDIELLA sp. 1 
Plate 30, B, figures 6-11 
This species is represented by only two specimens, a complete one and a 
brachial valve. The cardinal extremities are produced into small ears. The 
valves are moderately convex with the brachial valve somewhat transversely 
narrowly humped in the median region. At the front margin the costellae form 
fascicles of 2 or 3 costellae. 
Measuremenis in mm.—t116861a, length 7.0, brachial length 6.3, midwidth 
7.8, hinge width 7.1, thickness 3.9. 
Figured specimens.—116861a,b. 
Horizon and locality—Pogonip group (mottled zone 700 feet below the 
Eureka quartzite), in Nevada: Base of first ridge east of Frenchman Flat, Las 
Vegas (1°) Quadrangle. 
Genus ORTHIDIUM Hall and Clarke, 1892 
Orthidium Hatt and CLarKe, Pal. New York, vol. 8, pt. 1, p. 244, 1892—-ULricH and 
Cooper, Geol. Soc. Amer. Special Pap. 13, p. 110, 1938. 
ORTHIDIUM BELLULUM Ulrich and Cooper 
Plate 30, A, figures 1-5 
Orthidium bellulum Utricu and Cooper, Geol. Soc. Amer. Special Pap. 13, p. 111, pl. 16F, 
figs. 19-26, 1938. 
Types.—Holotype: 92848 ; paratypes : 92846a-c. 
Horizon and locality—Upper Pogonip group in Nevada: In Ikes Canyon on 
the east side of the Toquima Range, Roberts Mountains (1°) Quadrangle. 
ORTHIDIUM FIMBRIATUM Cooper, new species 
Plate 31, A, figures 1-6 
Shell small, resembling Orthidium bellulum; slightly wider than long; hinge 
narrower than the greatest shell width near the middle; sides gently rounded; 
cardinal extremities obtuse; anterior margin narrowly emarginate; valves un- 
equally convex, the pedicle valve having the greater convexity; surface costel- 
late and fimbriate; costellae about 4 to the millimeter at the front margin; 
lamellae about 2 to the millimeter ; frill of a specimen about 2 mm. long meas- 
uring I mm. 
Pedicle valve deep and strongly convex in lateral profile; greatest convexity 
in about the middle; anterior profile strongly convex and with a narrowly 
rounded summit creased by the narrow sulcus; lateral slopes flat, short, and 
steep; sulcus narrow, moderately deep and extending from the beak to the an- 
terior margin. Median region swollen to form an ill-defined fold; umbo narrow, 
