PART. .& CHAZYAN AND RELATED BRACHIOPODS—COOPER 685 
sockets between the tooth proper and its attachment to the valve. The individual 
muscle marks of this valve are not visible but the field is somewhat heart-shaped, 
large, and located just anterior to the delthyrial cavity. 
The hinge plate of the brachial valve is zygospiroid; divided into two oblique 
socket plates, short and narrow, that are attached to the valve on the sides of 
the notothyrial cavity. The adductor scars are small, and arranged on each side 
of a low median ridge that does not reach posteriorly to the notothyrial cavity 
and does not support the hinge plate. 
This species is characterized by its globular form and fairly large size. It 
differs from P. nasuta and P. microscopica in size and in having more prominent 
folding and costation. It resembles P. loeblichi but is a larger shell with more 
circular outline, less prominently elevated fold on the brachial valve, and the 
anterior third more deflected toward the pedicle valve. 
PROTOZYGA ROTUNDIFORMIS Cooper, new species 
Plate 140, J, figures 59-62 
Shell nearly circular in outline, slightly longer than wide; sides rounded, an- 
terior margin truncated; valves subequal, the pedicle valve having the greater 
depth ; paucicostate, the flanks marked by 1 or 2 obscure costae confined to the 
anterior and lateral margins. 
Pedicle valve moderately and evenly convex in lateral profile and with the 
maximum convexity at the middle; anterior profile strongly convex and with 
moderate slopes. Median region inflated ; umbonal region narrowly rounded, the 
rounding continued anteriorly but indistinctly as a low fold. Fold sulcate in 
anterior third, sulcus short, moderately deep, defined by a short costa on each 
side. Flanks gently inflated and with moderately steep slopes to the margins. 
Brachial valve moderately convex in lateral profile, maximum convexity just 
posterior to the middle; anterior profile broadly but fairly strongly convex ; 
median region strongly swollen; sulcus originating just anterior to the middle, 
poorly defined and indistinct ; sulcus occupied by a poorly defined low fold indis- 
tinct except at the margin. Flanks swollen and steep-sided. 
Measurements in mm.—Holotype, length 2.9, width 2.5, thickness 2.0. 
Type.—Holotype: 117249. 
Horizon and locality.—Lincolnshire formation (go to 120 feet above the “Mos- 
heim”) in Tennessee: On U. S. Highway 25E, 1 mile north of Indian Creek, 
Howard Quarter (T.V.A. 162-NW) Quadrangle. 
Discussion.—This species is characterized by its small size and globular form. 
It is much smaller than P. rotunda and differs further from that species in its 
more circular outline, stronger marginal costae, and the more nearly equal depth 
of its valves. The stronger costation distinguishes this species from P. nasuta 
and P. microscopica, both of which occur in formations near the age of that of 
P. rotundiformis. 
