PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 667 
sulcation characteristic of that genus. The brachial valve is sulcate, but the 
costae in the sulcus rise anteriorly to form a fairly prominent fold. These level 
off the sulcus and flanks at the front. Inside the brachial valve the parts of the 
hinge plate are short and delicate but the crura are rather shorter and stouter 
than those of Sphenotreta. Furthermore, the crura extend more directly toward 
the pedicle valve rather than obliquely forward as they do in Sphenotreta. 
Dorytreta reversa is placed in this genus with reservations. It is more strongly 
costate, and the inversion of the sulcus and fold are so exaggerated that some 
other category may ultimately be required for it. 
DORYTRETA BELLA Cooper, new species 
Plate 124, G, figures 39-43 
Shell small, triangular in outline, widest just anterior to the middle; sides 
forming an angle of 70°-80°; posterolateral margins gently rounded; anterior 
margin subtruncate. Anterior commissure sulcate in the young, uniplicate in 
the adult. Surface costate, 16 to 17 costae on an adult. 
Pedicle valve deeper than the brachial one, moderately convex in lateral pro- 
file and with the greatest convexity at about the middle. Anterior profile mod- 
erately and broadly convex. Umbonal region moderately and narrowly convex; 
median region swollen; median costa more prominent than its fellows on the 
umbo and median parts; depressed anteriorly with the two on each side of it to 
form a short and shallow sulcus. Flanks flattened and with moderately steep 
slopes. 
Brachial valve moderately convex in lateral profile, greatest depth slightly 
anterior to the middle; anterior profile broadly convex but narrowly depressed 
medially by the sulcus. Umbonal region somewhat flattened. Median region 
moderately swollen. Sulcus narrow, deepening to middle of valve where it is 
deepest but rising and becoming a low fold anteriorly. Fold composed of 4 
costae, the center 2 depressed slightly below the outer 2. Flanks moderately 
swollen and with steep sides. 
Measurements in mm.— 
Brachial 
Length length Width Thickness 
Holotype) |. wri teiens Sua Ahem. 3P. 6. 3.8 3.3 3.2 1.9 
Paratype: dsc. tsisadace: ald. awe 4.9 4.4 4.4 2.1 
Types—Holotype: 117191a; unfigured paratype: 117191b. 
Horizon and locality —McLish formation (upper part) in Oklahoma: From 
a roadside ditch in NW3 sec. 18, T. 2 N., R. 5 E., Pontotoc County. 
Discussion.—This species is larger, wider, and more numerously costate than 
the Tennessee species D. ovata. 
DORYTRETA OVATA Cooper, new species 
Plate 124, A, figures 1-13 
Shell small, elongate ovate in outline with the widest part at about the middle; 
sides rounded ; anterior margin somewhat truncate; widest at the middle; apical 
