918 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Types.—Holotype: 117826e; figured paratypes: 117826b,d,f; unfigured para- 
types: 117826a,c. 
Horizon and locality—Top of the Ridley formation in Tennessee: On east 
side of Marshall Knobs, 5 miles south of Murfreesboro, Murfreesboro (15’) 
Quadrangle. 
Discussion.—This species is characterized by low convexity and nearly square 
outline. It differs from O. speciosa in its lesser convexity and the flatness of the 
brachial valve. It approaches O. subplanodorsata but is even flatter than that 
species. 
OPIKINA SEPTATA Salmon 
Plate 230, B, figures 8-28 
Opikina septata SALMON, Journ. Paleont., vol. 16, No. 5, p. 591, pl. 87, figs. 1-4, 1942. 
Types—Holotype: 117829c¢; paratypes: 117829a,b; figured hypotypes: 
117827a,b, 117828, 117830. 
Horizon and locality—Lebanon formation (upper half=Doleroides zone) in 
Tennessee: On U. S. Highway 41, # mile south of Knox Branch, 9 miles 
southeast of Murfreesboro; U. S. Highway 70S, 0.8 mile west of Dry Branch 
of Cripple Creek; cut on U. S. Highway 241, 2.1 miles north of Bedford County 
line; U. S. Highway 41, 14 miles northwest of Mount Olivet, 10 miles southeast 
of Murfreesboro; Rutherford County. On U. S. Highway 70N opposite Fair- 
view Service Station, 4 mile west of Rome, Smith County; on U. S. Highway 
70S, + mile east of Readyville, Woodbury (15’) Quadrangle; Columbia, Maury 
County ; Lebanon, Wilson County. 
Discussion.—This species is characterized by its wide hinge and low convexity. 
It is quite different from O. transversa of the Wardell formation of Rye Cove 
which is much more convex and often more transverse. Opikina septata is sug- 
gestive of O. minnesotensis, but that species is differently shaped, less alate, and 
has a much larger muscle area in the pedicle valve. 
OPIKINA SPECIOSA Cooper, new species 
Plate 237, A, figures 1-19; plate 238, A, figures 1-7; plate 241, D, figures 20-28; 
plate 247, FE, figures 14-16; plate 249, A, figures 1-9 
Shell of about medium size for the genus; subrectangular in outline; wider 
than long and with the hinge usually forming the widest part ; cardinal extremi- 
ties subauriculate; sides slightly oblique; anterior margin narrowly rounded; 
costellae differentiated into strong and fine, numbering about 4 to the millimeter 
at the front margin; concentric fila strong. Concentric oblique wrinkles mark 
the posterior margin. 
Pedicle valve fairly strongly convex in lateral profile and with the maximum 
convexity located just anterior to the middle; posterior three-fifths gently con- 
vex in lateral profile; anterior two-fifths strongly bent at an angle varying from 
100° to 120° toward the brachial valve; anterior slope rounded and steep; lat- 
eral slopes longer than the anterior one and much less steep. Interior with muscle 
