PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 677 
Pedicle valve strongly convex in lateral profile with the maximum convexity 
in the posterior half; anterior commissure somewhat narrowly convex and with 
long, steep lateral slopes. Umbo narrowly convex; median region narrowly in- 
flated; anterior third marked by a low, poorly defined fold. 
Brachial valve shallow, gently convex in lateral profile; anterior profile barely 
concave to broadly and gently convex; umbonal region broadly and gently con- 
vex; sulcus narrow and shallow, originating near the middle and almost com- 
pletely filled by 2 costae. Sulcus shallow throughout its length. Flanks gently 
inflated. Spire as described for the genus. 
Measurements in mm.—Holotype, length 4.5, width 3.9, thickness 2.2. 
Types.—Holotype: 117239c; unfigured paratypes: 117239a,b. 
Horizon and locality—Bromide formation (Mountain Lake member) in Okla- 
homa: In the road cut on Oklahoma Highway 18, 1.8 miles south of Sulphur, 
Murray County ; Spring Creek, sec. 17, T. 2 S., R. 1 W., Murray County ; on the 
north side of Falls Creek along the road to the Baptist Camp, NE4SE# sec. 32, 
T.1S., R.2E., Murray County; from deep well at 3,240 to 3,244 feet in Mid- 
continent Petroleum Corporation well, sec. 22, T. 4 N., R. 3 E., Pottawatomie 
County. 
Discussion—This species is characterized by its strong costae and elongate 
form. In the latter respect it is like P. elongata, but that species is not so strongly 
costate. It differs from other Oklahoma species and the known species outside 
of Oklahoma by the moderate development of the fold and sulcus and the strong 
costation of these features. 
PROTOZYGA ELONGATA Cooper, new species 
Plate 140, E, figures 27-37; plate 143,I, figures 41-46 
Shell small, elongate oval in outline with the greatest width at about the 
middle; sides gently rounded; anterior margin truncated. Surface marked by 
fine growth lines and the flanks by 2 to 4 obscure costae. 
Pedicle valve fairly strongly convex and with the greatest convexity at about 
the middle; beak elongated; umbo narrowly rounded and extended anteriorly 
as a prominent fold to the anterior quarter where a shallow sulcus divides the 
fold into 2 narrowly rounded costae. Flanks concave and steep sided. Marginal 
fold between umbo and shoulder fairly strong. 
Brachial valve with less depth and less convexity than the pedicle valve and 
with the maximum convexity at about the middle. Umbonal and median regions 
somewhat swollen. Fold narrow, originating at about two-thirds the length from 
the beak of the brachial valve. Flanks convex but with moderate slopes to the 
extremities. 
Measurements in mm.—Holotype, length 3.1, width 2.3, thickness 1.7. 
Types.—Holotype: 117241a; figured paratypes: 117241b,c, 111408a,b. 
Horizon and locality—Bromide formation (Mountain Lake member—Dole- 
roides zone=bryozoan zone) in Oklahoma: Along the old road up the hill 
northwest of the old Galbraith Hotel, sec. 32, T. 1 S., R. 8 E., Johnston County ; 
