PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER O13 
OPIKINA MAJA Cooper, new species 
Plate 236, D, figure 14 
Shell large for the genus, subquadrate in outline, with the length and width 
nearly equal in the adult; sides gently rounded, subparallel; anterior margin 
somewhat narrowly rounded; hinge narrower than the midwidth in the adult 
but wider than the midwidth in young; cardinal extremities rounded. Four to 
six costellae in 1 mm. at the front margin; posterior margin with oblique 
wrinkles. 
Pedicle valve fairly evenly convex in lateral profile, with the maximum con- 
vexity just anterior to the middle; umbonal and posterior regions swollen; an- 
terior profile strongly domed and with long, moderately steep sides. Narrow 
swelling at umbo. Median region strongly swollen; anterior slope gently convex 
in profile, long and steep; interarea short. Interior with large flabellate muscle 
field occupying less than half the inner surface. 
Brachial valve with maximum depth at or just anterior to the middle; pos- 
terior half gently concave; sides and anterior margin moderately bent in the 
direction of the brachial valve. 
Measurements in mm.—Holotype, length 42.8, brachial length 40.2, midwidth 
43.1, hinge width 32.5?, thickness 9.7, height 17.7. 
Types.—Holotype: 117819; unfigured paratype: 117820. 
Horizon and locality—‘Lebanon formation” = Ridley formation in Kensing- 
ton (T.V.A. 206-SE) Quadrangle, Georgia: From a road cut on U. S. High- 
way 27, on the north bank of Chickamauga Creek, 14 miles northeast of Pond 
Spring. 
Discussion.—This is the largest of the species referred to Opikina. Although 
the proportions approach Macrocoelia, the geniculation of the brachial valve as 
revealed by a brachial interior (117820a) is like that characteristic of Opikina. 
OPIKINA MATUTINA Cooper, new species 
Plate 245, C, figures 13-20 
Small for the genus, subrectangular in outline; wider than long and with the 
hinge forming the widest part; cardinal extremities acute to auriculate; sides 
gently rounded; anterior margin broadly rounded; surface costellate as usual 
in the genus, about 6 to the millimeter at the front margin. Oblique wrinkles 
present on posterior margin. 
Pedicle valve unevenly convex in lateral profile with the visceral region occu- 
pying the posterior two-thirds, gently convex; angle of geniculation about 100° ; 
trail short, steep, and nearly flat in profile; umbo narrowly folded at the beak 
and forming a short, indistinct fold; interarea short. Interior with large muscle 
field ; diductors subflabellate. 
Brachial valve with visceral region flattened but anterior margin strongly 
deflected toward the brachial valve to form a deep concavity; sides much less 
strongly deflected than the anterior margin; umbo sulcate. Interior with usual 
septa thickened and partly covered by adventitious shell. 
