PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 905 
Types.—Holotype: 117799a; figured paratypes: 117799b-e. 
Horizon and locality Edinburg formation (Cyrtonotella zone) in Strasburg 
(15’) Quadrangle, Virginia: In the ravine at the switch about 4 mile east of 
Strasburg Junction; Tumbling Run, 14 miles southwest of Strasburg. 
Shippensburg formation (Echinosphaerites zone) in Maryland: On the west 
bank of Conococheague Creek on U. S. Highway 40, 7 miles west of Hagers- 
town, Williamsport (15’) Quadrangle. 
Discussion—This species is characterized by its moderate size, low convexity, 
and fairly strong costellae. The general form of the shell is suggestive of 
O. speciosa and O. formosa, but these are larger and more strongly geniculated 
species. It is more convex and more strongly ornamented than O. minnesoten- 
sis. Opikina varia from Alabama is somewhat similar in size and form but is 
more strongly geniculated and the interior of the brachial valve has the septa 
more strongly developed. 
OPIKINA CLARA (Okulitch) 
Rafinesquina clara Oxu.ircu, Canadian Field-Nat., vol. 49, No. 6, p. 97, pl. 1, fig. 1, 1935. 
Opikina clara (Okulitch) Satmon, Journ. Paleont., vol. 16, No. 5, p. 597, pl. 87, fig. 28, 1942. 
Type.—Holotype: Peter Redpath Mus. 
Horizon and locality —Leray =Chaumont in Quebec: At Pointe Claire. 
OPIKINA DORSATIFORMIS Cooper, new species 
Plate 237, B, figures 20-28; plate 242, B, figures 6-10 
Small for genus, subquadrate; length and width about equal; sides gently 
rounded, subparallel; anterior margin narrowly rounded; hinge narrower than 
the midwidth ; cardinal extremities rounded. From 3 to 5 costellae in I mm. at 
the front margin; short wrinkles appear on the posterior margin. 
Lateral profile strongly convex; visceral region not strongly differentiated 
from the trail; geniculation occurring about 5 mm. anterior to the beak; visceral 
region gently convex and provided with obscure concentric wrinkles; angle of 
geniculation less than a right angle; trail long and moderately convex; lateral 
slopes precipitous. 
Brachial valve deeply concave and deepest at the middle; umbo sulcate, the 
sulcus extending for a short distance anteriorly; sides and anterior margin 
strongly deflected toward the brachial valve and forming a high rim around the 
median concavity. 
Measurements in mm.— 
Brachial Hinge Thick- Trail 
Length length Midwidth width ness Height length 
olotypeis sats. raetses 13.6 11.6 14.2 muy, 3.9 7.4 17.5 
Paratype (117800)... 10.4 2 12.4 11.9 iy 4.7 10.0 
Types.—Holotype: 117801 ; figured paratype: 117800. 
Horizon and locality—Edinburg formation (Cyrtonotella and Nidulites 
zones) in Strasburg (15’) Quadrangle, Virginia: Just east of a small ravine on 
