920 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
“Lebanon” limestone= Ridley formation= Wardell formation in Georgia: In 
a quarry 14 miles south-southeast of Cove Church, Kensington (T.V.A. 206-SE) 
Quadrangle; on U. S. Highway 27, 1 mile north of Rock Spring, Nickajack Gap 
(T.V.A. 113-SW) Quadrangle. 
Discussion—This species is abundant and widespread in the Wardell forma- 
tion in Virginia and Tennessee. It resembles O. transitionalis Okulitch, but sig- 
nificant differences between the two species can be detected. Opikina speciosa as 
defined and identified herein is a variable species and may ultimately be further 
split. The specimens from the Ridley formation of the central basin of Tennessee 
appear to be somewhat narrower than those from the Wardell formation along 
the Cumberland Front and in Sequatchie Valley. However, length-width index 
of these narrow forms differs 0.07 from the broadest specimens. 
Opikina speciosa is suggestive of O. transitionalis, O. inquassa, and O. formosa. 
Comparison with the last species is made above. From O. inquassa the Appa- 
lachian species differs in having its geniculation farther anterior to the beak than 
in the Minnesota species. Thus the maximum convexity is farther anterior than 
in the Minnesota species. The anterior trail of O. speciosa is more swollen and 
steeper than that of O. inquassa. According to Salmon (1942, p. 596) O. transi- 
tionalis possesses “sharply projecting ears and a sinuous lateral margin.” These 
are not features of O. speciosa. Dr. Salmon states further that the genicula- 
tion in O. inquassa occurs farther toward the anterior than in O. transitionalis. 
This feature makes comparison with O. speciosa still more remote because its 
geniculation takes place farther anterior than it does in O. inquassa. 
Opikina speciosa is more strongly geniculated and farther from the beak than 
in O. lirata. The Oklahoma Opikinas are all different from O. speciosa. 
OPIKINA SUBPLANODORSATA Cooper, new species 
Plate 241, C, figures 14-19 
Shell of about medium size for the genus, subquadrate; slightly wider than 
long, the hinge usually narrower than the width at the middle; sides gently 
rounded, subparallel; anterior margin narrowly rounded; cardinal extremities 
obtuse. Costellae fine and thin, 3 or 4 to a millimeter at the front margin. 
Pedicle valve unevenly convex in lateral profile, the posterior three-fifths 
nearly flat except near the beak where it is somewhat swollen ; anterior two-fifths 
gently rounded but forming a fairly steep anterior slope bent about 115° from 
the posterior part. Geniculation prominent in the adult; sides with moderately 
steep slopes. 
Brachial valve gently and evenly concave throughout its length; maximum 
concavity located at the middle or slightly anterior to it. Sides and anterior 
margins bent only slightly toward the brachial valve. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
15) (0) 4 0 a a 22.7 21.0 24.6 20.4 6.3 8.2 
Paratype (117840c)..... 21.8 IG.8) \\\0\ e630 22.0 5.6 7.4 
