PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER QI7 
Lateral profile unevenly convex, narrowly rounded at about the middle, the 
angle of geniculation about 95° ; anterior profile narrowly convex ; visceral region 
gently swollen and gently convex in profile; anterior slope gently convex but 
long and steep; lateral slopes long and steep, about equal to the anterior slope; 
interarea moderately long. Interior with elongate diductors and large adjustor 
scars; pallial marks well developed. 
Brachial valve gently concave in the visceral region; deepest just anterior to 
the middle; sides and anterior margin strongly and abruptly bent toward the 
brachial valve to surround the visceral region. 
Measurements in mm.—Holotype, length 9.5, brachial length 8.6, midwidth 
10.4, hinge width 10.5, thickness 4.2, height 6.0. 
Types.—Holotype: 117825a; figured paratype: 117825b. 
Horizon and locality—Benbolt formation (base) in Virginia: 0.2 mile south 
of the middle fork of Moccasin Creek, 14 miles south of Hansonville, Hanson- 
ville (T.V.A. 205-SW) Quadrangle. 
Discussion.—This species is unlike all others herein described in its small 
size and strong convexity. It is much smaller than O. dorsatiformis or O. parvula 
which are both small species. The shell is thick and the pallial marks strongly 
impressed. 
OPIKINA QUADRATA Cooper, new species 
Plate 241, B, figures 9-13 
Shell of about medium size, with the length and width about equal; sides 
gently rounded, subparallel ; anterior margin somewhat narrowly rounded ; hinge 
variable, generally less than the midwidth in the adult; costellae numbering 
about 3 of the stronger ones to 1 mm. at the front margin. 
Pedicle valve fairly evenly and gently convex in lateral profile and with the 
maximum convexity just anterior to the middle; anterior profile broadly and 
gently convex, not domed ; umbonal region somewhat broadly swollen and mod- 
erately elevated above the posterolateral regions; median and anterior region 
moderately swollen; anterior slope about equal to the lateral slopes but some- 
what steeper. Muscle area large and not quite reaching the middle. 
Brachial valve deepest in the midregion but not of great depth anywhere on 
the valve; posterior region gently concave and deepening toward the middle; 
margins moderately bent toward the brachial valve to form a gently sloping 
rim. Interior with septa not strongly developed and adductor ridges and margins 
thickened. Subperipheral rim moderately thickened. 
Measurements in mm.— 
Brachial Hinge Thick- 
Length length Midwidth width ness Height 
Holotype das ticicicaesiss cass ? 20.0 21.5 20.5 ? ? 
Paratype (117826a)...... ? 19.3 20.3 21.7 ? ? 
Ht (117826b)...... 20.5 ? 23:4 20.6 P 5.3 
4 (117826) 2s42 ? 19.1 20.0 21.9 ? ? 
i’ (7178260) )s.\2.5: 20.0 f 20.9 19.4 ? 4.3 
