PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 339 
impressed adductor field; brachiophores short and stout, supported by shell ma- 
terial filling the notothyrial cavity ; cardinal process long and slender. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
EAGUIGEYDG. ce iwicscicc Gus « 0.4 8.4 10.2 9.9 5.3 
Paratype (116850c)... 7.8 7.0 8.9 9.0 3.9 
$s (116850d)... 10.9 ? 12.1 12.9 2.4 
Types.—Holotype: 116859a ; figured paratypes: 116859b-e; figured specimen : 
117981a. 
Horizon and locality—Orthidiella zone of the Pogonip group in Nevada: At 
the Narrows, 2 miles up Whiterock Canyon, Roberts Mountains (1°) Quad- 
rangle. Mottled zone 700 feet below the Eureka quartzite: Base of first ridge 
east of Frenchman Flat, Las Vegas (1°) Quadrangle. 
Discussion.—This species is very close to O. longwelli from southern Nevada 
and agrees with it in many details. It differs, however, in the much finer orna- 
mentation and the lack of any tendency for the costellae to bundle. The propor- 
tions are slightly different, and the species tends toward a larger size than 
O. longwelli. 
ORTHIDIELLA EXTENSA Ulrich and Cooper 
Plate 30, E, figures 21-32 
Orthidiella extensa ULricu and Cooper, Geol. Soc. Amer. Special Pap. 13, p. 1009, pl. 16C, 
figs. 10, II, 15-17, 1938. 
Types—Holotype: 91297; paratypes : 91297a,b; figured hypotypes : 116857a-c, 
e-g; unfigured hypotype: 116857d. 
Horizon and locality—Upper Pogonip group (mottled zone about 700 feet 
below the Eureka quartzite) in Nevada: Near the base of the first ridge east of 
Frenchman Flat, Las Vegas (1°) Quadrangle. 
ORTHIDIELLA LONGWELLI Ulrich and Cooper 
Plate 30, D, figure 20 
Orthidiella longwelli ULricnH and Cooper, Geol. Soc. Amer. Special Pap. 13, p. 109, pl. 17D, 
figs. 15-33, 1938. 
O. striata ULricH and Cooper, Idem, p. 110, pl. 16B, figs. 2-4, 7-9, 1938. 
Examination of large suites of this species shows that O. striata and O. long- 
welli are in reality the same. Inasmuch as O. longwelli is the genotype the other 
species is here suppressed. 
Orthidiella longwelli shows considerable variation in the costellation, outline, 
and profiles. One example is fairly coarsely costellate, has narrow ears and is 
very robust in the umbonal region. The latter feature comes about by swelling 
in young stages and a rapid contraction near the middle of the valve. 
Types.—Holotype: 91299 ; paratypes : 91300a-g ; holotype of O. striata: 91303 ; 
paratypes O. striata: 91304a,b. 
Horizon and locality—Pogonip group (mottled zone 700 feet below the Eureka 
