PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 129 
PIOCHE DISTRICT, NEVADA 
The Tank Hill formation is named from Tank Hill in the Ely Springs 
Range west of Pioche, Nev. The formation also appears at the north end of 
the Bristol Range. It consists of 450 feet of gray thin-bedded limestone, con- 
glomeratic in the lower part. The upper 50 feet is shaly limestone with abundant 
fossils. Brachiopods are: 
Hesperinia kirki Cooper 
Orthambonites sp. 
CALIFORNIA 
Phleger (1933, p. 2) proposed the Mazourka and Barrell Spring formations 
for Ordovician rocks exposed in the Inyo Range, east-central California. 
Mazourka formation.—This formation consists of argillaceous shales and 
limestones 675 feet thick. Fossils are not well preserved, but several brachiopods 
were collected and some new species described, as follows: 
Crania sp. 
Orthis minusculus Phleger = Orthambonites minusculus (Phleger ) 
Plectorthis mazourkaensis Phleger 
P. patula (Phleger) 
Triplesia sp. = syntrophoid 
Besides the brachiopods listed, interesting trilobites were collected indicating 
correlation of these beds with the Oil Creek of Oklahoma and the Anomalorthis 
zone of the Pogonip. These trilobites are Pseudomera barrandei (Billings), 
Encrinurus hastula Phleger, and E. octonarius Phleger, the latter two being 
referable to the genus Ectenonotus which occurs in the East in the Table Head 
series and Mystic boulders. 
Barrel Spring formation.—This formation was also proposed by Phleger 
(1933, p. 5) for 130 feet of quartzites, impure limestones, and argillaceous shales. 
Three brachiopods are listed: 
*Orthis tricenaria Conrad = Hesperorthis ? 
O. decipiens Phleger = Hesperorthis ? decipiens (Phleger) 
Plectambonites angulatus Phleger = Valcourea angulata (Phleger) 
The identification of Orthis tricenaria Conrad is almost certainly a mistake, 
but the identification may indicate some other species of Hesperorthis. Although 
the description of Plectambonites angulatus states that the ‘Pedicle valve [is] 
evenly convex, but gently arched along the median line from beak to front,” the 
figure of the one cotype illustrated gives the impression that the specimen is 
really nearly flat or gently concave. Furthermore, the long slits representing the 
pits formed by the dental plates in the impression and the muscle scars suggest 
Valcourea rather than Plectambonites. The latter name is undoubtedly used in 
the old sense and would now be called Sowerbyella, inasmuch as true Plectambo- 
nites is at present unknown on this continent. 
The lithology and the few fossils known from the Barrel Spring formation 
