904 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Pedicle valve with moderately convex visceral region, rounded geniculation, 
and steep, moderately long trail. Angle of geniculation about 96° ; geniculation 
occurring 5 to 6 mm. anterior to the beak; sides steep; umbo narrowly convex ; 
interarea short. 
Brachial valve with gently concave visceral region; deepest anterior to the 
middle just below the steep trail; sides moderately deflected toward the brachial 
valve; anterior margin strongly deflected; internal septa mostly covered by 
adventitious shell. 
Measurements in mm.—Holotype, length 10.5, brachial length 9.3, midwidth 
13.6, hinge width 16.4, thickness 2.0?, height 4.8, trail length 7.0. 
Types.—Holotype: 117797c; figured paratype: 117797b; unfigured paratype: 
1177972. 
Horizon and locality—Edinburg formation (Nidulites zone) in Strasburg 
(15’) Quadrangle, Virginia: 100 yards south of the entrance to Battlefield 
Crystal Caverns on U. S. Highway 11, 1 mile north of Strasburg; along 
Tumbling Run, 14 miles southwest of Strasburg. 
Discussion—This species is characterized by the ears on the cardinal ex- 
tremities, small size, and geniculation near the middle. The species may be con- 
fused with O. dorsatiformis and O. parvula which has about the same size. It 
differs from the former in being much less convex and in not geniculating at so 
early a stage of growth as O. dorsatiformis. It differs from O. parvula in having 
its place of geniculation at the middle rather than anterior to the middle and 
in having more pronounced ears. 
OPIKINA BELLULA Cooper, new species 
Plate 242, D, figures 14-25 
Small for the genus, subrectangular, wider than long with the hinge forming 
the widest part; cardinal extremities subauriculate ; sides gently rounded, gently 
oblique; anterior margin narrowly rounded; surface strongly costellate, costellae 
on visceral area with strong costellae separated by numerous fine ones but trail 
marked by strong costellae with the finer ones distinctly subordinate; 2 or 3 of 
the stronger costellae in 1 mm. at the front margin. Strong wrinkles on posterior 
margins. 
Pedicle valve unevenly convex in lateral profile, the visceral region being 
nearly flat to gently convex but the front third strongly angulated about 10 mm. 
anterior to the beak; angle of geniculation about 110°; umbo narrowly swollen, 
the swelling continued anteriorly as a low fold. Visceral disk region gently 
swollen ; anterior and lateral slopes short and steep. 
Brachial valve with visceral region concave and with lateral and anterior mar- 
gins fairly strongly deflected toward the brachial valve. 
Measurements in mm.— 
Brachial Hinge  Thick- Trail 
Length length Midwidth width ness Height length 
EDOIGtHOS ME ees ices Ce oes 15.3 ? 17.8 19.2 ? SO" 8 Fee 
Paratype (117799b).... 14.9 13.7 18.0 19.0 ? 5.0 7.5 
