PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER go09 
Pedicle valve moderately convex in lateral profile with the maximum convexity 
in the anterior third ; posterior two-thirds gently convex ; anterior profile broadly 
and gently convex; umbo narrowly swollen to form a short, low fold; median 
region gently swollen; anterior third moderately swollen and bent toward the 
brachial valve to form a short and steep anterior slope; lateral slopes long and 
gentle. 
Brachial valve gently concave, the maximum concavity at about the middle; 
posterolateral regions flattened to form the ears; sides moderately, and anterior 
margin fairly strongly, bent in the direction of the brachial valve. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
Erolotype: sss eGo se Oe 19.8 18.4 29.5 40.6 4.7 6.9 
Paratype (123268a)..... 19.8 18.7 27.0 ? 3.6 6.3 
Types.—Holotype: 123268b ; figured paratype: 123268a ; unfigured paratype: 
123268c. 
Horizon and locality Bromide formation (Pooleville member) in Oklahoma: 
3 miles northeast of Springer, Carter County. 
Discussion.—This species is unlike any other described herein in the great 
lateral extension of the hinge to form long, blunt ears. The species, by the simi- 
larity of its ornamentation to that of O. formosa and expatiata, is undoubtedly 
related to those species. 
OPIKINA FORMOSA Cooper, new species 
Plate 243, B, figures 9-17; plate 243, C, figures 18-28 
Shell of about medium size for the genus, subquadrate, slightly wider than 
long; hinge equal to or slightly less than the midwidth; cardinal extremities 
nearly a right angle; sides subparallel; anterior margin somewhat narrowly 
rounded. Costellae strong, alternating fine and strong on the posterior and not 
strongly differentiated at the front margin where 4 costellae appear in the space 
of I mm. 
Pedicle valve unevenly to fairly evenly convex in lateral profile, the maximum 
convexity just anterior to the middle; anterior profile strongly domed. Beak 
prominent ; umbo narrowly swollen and forming a low, short fold; posterior half 
gently to moderately swollen; angle of geniculation varying from 110° to 120°; 
anterior slope or trail steep and nearly flat to gently convex in profile; sides 
steep. Interior not known. 
Brachial valve gently concave in the posterior half, more deeply concave an- 
terior to the middle where the valve is deflected steeply toward the brachial 
valve; umbo somewhat broadly concave; sides fairly strongly deflected in the 
direction of the brachial valve. Interior with thickened and beaded subperipheral 
rim; 5 septa well developed; cardinal process stout and long. 
