PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 357 
Measurements.— 
Brachial Hinge 
Length length Width width Thickness 
folotypel, i sake sa.) 13.8 11.7 15.3 14.1 6.7 
Basatype (109992d).. 13.5 10.9 14.0 12.4 6.0 
(109994c).. 10.5 8.7 10.3 11.3 5.7 
* (109994b).. 10.4 8.7 ht 11.8 5.0 
a (109988a).. 14.3 11.4 14.7 14.4 6.9 
8 (109987d).. 16.2 13.3 17/2 15.6 7.0 
s (109987c).. 14.0 11.1 15.8 152 6.5 
Types.—Holotype : 109987b ; figured paratypes : 109987a,d, 109992e, 109994b ; 
unfigured paratypes: 109987c,e,f, rog9g88a-f, 10g992a-d, 10g994a,c-h, 116922. 
Horizon and locality—Bromide formation (Pooleville member-O-ropflecia 
gouldi zone) in Oklahoma: At Rock Crossing of Hickory Creek, about center 
sec. 35, [. 5 S., R. 1 E.; ona branch of Hickory Creek, NW+# sec. 26, T. 5 S., 
R. 1 E., Criner Hills, Carter County. Upper Bromide formation in Oklahoma: 
Just west of the road on the Russell Ranch, SE# sec. 3, T. 2 S., R. 3 E., Murray 
County. 
Discussion.—This species is characterized by having its length and width 
nearly equal, broad costae, and deep brachial sulcus. It is closest to H. australis 
but differs in its more quadrate outline and the greater development of the 
sulcus. 
HESPERORTHIS TENUICOSTATA Cooper, new species 
Plate 54, E, figures 22-40; plate 82, B, figures 7-11 
Shell of about medium size for the genus, a little wider than long. Width of 
hinge about equal to width of valve at middle or somewhat less. Lateral mar- 
gins very slightly to moderately curved; front margin broadly rounded. Anterior 
commissure slightly sulcate. Apical angle about 110°. Surface marked by about 
29 direct, elevated, and narrowly rounded costae with interspaces about as wide 
as the width of a costa. 
Pedicle valve moderately convex with the greatest convexity in the posterior 
half; anterior profile strongly convex. Median portion swollen; flanks gently 
convex and moderately steep. Interarea gently curved, strongly apsacline. Beak 
a little incurved. Interior with small elongate muscle area. 
Brachial valve slightly convex in lateral profile; slightly indented medially in 
anterior profile. Sulcus narrow, very shallow. Flanks bounding sulcus very 
slightly swollen. Posterolateral extremities slightly depressed. Notothyrial cavity 
shallow ; brachiophores long. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Halotypenink... 12) sis 10.8 9.1 THe 9.8 5.0 
Paratype (109973a).. I1.5 9.5 12.5 10.6 5.9 
Types.—Holotype: 116924; figured paratypes: 109970a, 109973a, 116923; 
unfigured paratypes: 109970b-d, 109973b-e. 
