PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 499 
Discussion—This species attains a fairly large size and is therefore compara- 
ble to S. halli, S. transversus, and S. rectangulatus. It is characterized by strong, 
direct, and somewhat distant costae, strong fold and sulcus, and nearly catacline 
interarea. Skenidioides oklahomensis differs from S. halli in its larger size, 
stronger and more distant costae, catacline interarea, and narrower and deeper 
sulcus. Skenidioides transversus is more transverse, as its name implies, than 
the Oklahoma species, and its fold and sulcus are much less pronounced. Skeni- 
dioides rectangulatus approaches the Oklahoma species in size, costation, and 
strength of fold and sulcus but differs in proportions. Its lateral extremities are 
squarer and the outline more quadrate. 
SKENIDIOIDES PERFECTUS Cooper, new species 
Plate 97, E, figures 49-54; plate 98, D, figures 18-23 
Shell of about medium size for the genus, wider than long, not quite twice as 
wide as long ; cardinal extremities acute; sides sloping steeply toward the middle 
and gently rounded; anterior margin nearly straight or medially emarginate. 
Anterior commissure deeply sulcate. Surface costate, 6 costae on the fold, 8 to 
g on the flanks and 6 to 8 in the sulcus; costae and intercostal spaces of about 
equal width. 
Pedicle valve gently convex in lateral profile; anterior profile subcarinate ; 
fold prominent, elevated, formed by a fascicle of costae; fascicle formed by a 
single rib which bifurcates after 1 mm., another bifurcated median rib located 
inside the bifurcation; median fascicle with a costa on each side at the base of 
the fold. Flanks bounding fold barely convex. Interarea long, posterior margin 
nearly straight, and beak low and inconspicuous; interarea nearly catacline. 
Brachial valve in lateral profile flat in the posterior half but convex toward 
the pedicle valve in the anterior half; anterior profile perceptibly convex but with 
the median region narrowly sulcate. Sulcus originating at the beak which is 
smooth and flat ; sulcus deepening and widening anteriorly but not equaling half 
the width at the front margin; flanks bounding sulcus perceptibly convex; pos- 
terolateral extremities gently concave. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness 
EVOIOLEY Oh else asa hugs tee, > 2.2 2.2 3.4 3.9 1.4 
Paratype (117081) ..... 2.6 2.4 3.8 4.1 1.6 
Types.—Holotype: 117080; unfigured paratype: 117081; figured specimens: 
117082b,c, 109987d. 
Horizon and locality—Bromide formation (Pooleville member—O-xoplecia 
gouldi zone) in Carter County, Okla.: at Rock Crossing of Hickory Creek, ap- 
proximately center sec. 35, T. 5 S., R. 1 E., Criner Hills; NW4 sec. 26, T. 5 S., 
R. 1 E.; SE4 sec. 32, T. 2 S., R. 2 E., about 2 miles northeast of Springer. 
Discussion—Skenidioides perfectus is a small species suggesting S. anthonen- 
sis, S. costatus, S. convexus, and S. rectangulatus. The Oklahoma species dif- 
