908 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Pedicle valve moderately convex in lateral profile, the maximum convexity 
located anterior to the middle; anterior profile broadly domed ; valves not genicu- 
lated but curved just anterior to the middle, the angle of the curvature being 
about 130°. Beak small, umbo marked by a poorly defined narrow, low fold; 
posterior half gently swollen; anterior half strongly swollen and with a long 
steep anterior slope; lateral slopes long and steep. Interarea moderately long; 
pseudodeltidium of many specimens marked by groove. Interior not known. 
Brachial valve gently concave, most concave at about the middle; sides and 
anterior margin moderately to strongly deflected toward the brachial valve. Pos- 
terolateral region moderately flattened. Interior with unusually low septa and 
ridges; brachiophores small and bladelike and with only a modest development 
of the socket cups; subperipheral rim strong in old shells. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
Brolotyperii es isso. 28a ode 23.4 22.3 30.2 29.1 3.8 7.5 
Paratype (117807b)..... 19.0 17.5 20.8 23.6 2.8 4.6 
rh (117807d)).52... 19.2 18.1 22.3 227 3.0 6.0 
s (117807e)..... 19.9 17a 23.4 27.1 2.5 5.0 
a (r178075)) Ash 23.0 21.4 26.8 28.9 ? 6.1 
Types.—Holotype: 117807a; figured paratypes: 117807b,c; unfigured para- 
types: 117807d-f. 
Horizon and locality. Bromide formation (Mountain Lake member) in Mur- 
ray County, Oklahoma: On the east side of the road cut on Oklahoma High- 
way 18, NW sec. 11, T.1 S., R. 3 E., 1.8 miles south of Sulphur ; Spring Creek, 
ig ts ey pa Wd pres ete 5 a ib fs 
Discussion.—This species is characterized by its fairly large size, moderate 
but uneven convexity, width greater than the length, and the broad, open con- 
cavity of the brachial valve. This species differs from O. formosa in its greater 
size, more openly concave brachial valve, more subdued character of the septa 
of the brachial interior, and less pronounced ears. It is similar in size and form 
to O. lirata from the Decorah (Ion) of Minnesota but is more convex anteriorly, 
has a longer interarea, and is less deeply concave. Some specimens suggest 
O. speciosa, but that species is generally less wide, more strongly geniculated, 
and more convex anteriorly. 
OPIKINA EXTENSA Cooper, new species 
Plate 243, A, figures 1-8 
Shell moderately large for the genus, wider than long and with extended and 
alate hinge; cardinal extremities acute; sides strongly oblique; anterior margin 
broadly rounded; costellae of pedicle valve stronger and more even than those 
of the brachial valve and numbering 3 to the millimeter; costellae of brachial 
valve strongly differentiated into fine and strong, 2 of the latter in I mm. at the 
margin and separated by 2 or 3 of the finer costellae. Posterior margins with 
oblique wrinkles. 
