906 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
the north side of the road along Tumbling Run, 14 miles southwest of Strasburg ; 
in the ravine at the switch about 4 mile east of Strasburg Junction. 
Discussion.—This species is recognized by its small size and nearly hemispheri- 
cal lateral profile. It is most like O. dorsata from the Kuckers formation of 
Estonia but differs in having squarer outline and wider hinge than the Estonian 
species. Furthermore, the Estonian species is somewhat more convex and 
smaller. 
OPIKINA ? DUBIA Cooper, new species 
Plate 246, D, figures 12-14 
Shell small, length and width about equal; sides nearly parallel ; hinge slightly 
wider than or equal to the midwidth; anterior margin narrowly rounded; sur- 
face costellate, 4 or 5 costellae in 1 mm. at the front margin. 
Pedicle valve with lateral profile uneven, the umbonal region slightly convex, 
the area just anterior to the middle slightly concave, and the marginal regions 
abruptly bent in the direction of the brachial valve; anterior profile broadly and 
slightly convex. Umbonal region gently convex; region just posterior to the 
margin gently concave; margins bent toward the brachial valve narrowly and 
abruptly ; lateral and anterior slopes short and precipitous. 
Brachial valve with concave umbo but gently convex visceral region ; margins 
bent abruptly toward the brachial valve; postmarginal areas narrowly concave. 
Measurements in mm.— 
Brachial Hinge Thick- 
Length length Midwidth width ness Height 
Holotype (pedicle valve).. 14.4 ? 16.2 16.0 ? 2.5 
Paratype (brachial valve). ? 13.4 14.6 14.9 ? ? 
Types.—Holotype: 123274a; figured paratype: 1232738. 
Horizon and locality—Botetourt formation in Virginia: In Lexington (15’) 
Quadrangle, 1 mile northwest of Lexington; 2 miles south of Stag Back Moun- 
tain, 7 miles north-northeast of Lexington. Near Cedar Grove Church and 
School, 14 miles southeast of Harrisonburg, Harrisonburg (15’) Quadrangle. 
Discussion.—The almost flat to gently concave lateral profile and strong mar- 
ginal geniculation of this species separate if from all other known species of the 
genus except O. nasuta (which see). No interiors of this are known. The 
generic assignment is therefore questioned because of its peculiar form. 
OPIKINA EXIMIA Cooper, new species 
Plate 240, B, figures 8-18 
One of the largest of known species; subquadrate, length and width nearly 
equal; sides gently curved, subparallel; hinge forming the widest part; cardinal 
extremities auriculate; anterior margin narrowly rounded. Costellae well dif- 
ferentiated, 2 of the stronger ones in I mm. at the front margin. Strong wrinkles 
on posterior margins. 
Pedicle valve of uneven convexity in lateral profile, the posterior two-thirds 
gently convex and the anterior third fairly strongly geniculated ; anterior profile 
