PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 393 
Horizon and locality—Oil Creek formation in Carter County, Okla.: Along 
Henryhouse Creek; on U. S. Highway 77, sec. 25, T. 2 S., R. 1 E., 2 to 3 miles 
north of Springer; north end of Criner Hills. In Murray County, Okla.: in 
NE} sec. 22, T. 2 S., R. 1 E., 4 to 5 miles due north of Glenn; along the road 2 
miles southwest of Nebo; second dam on Spring Creek; 1 mile northwest 
of Hickory ; section on Falls Creek. In Johnston County, Okla.: on west branch 
of Sycamore Creek, sec. 27, T. 3 S., R. 4 E.; middle of the south side sec. 34, 
T.2N., R. 6 E., 1 mile southwest of Franks. 
Discussion.—This species is abundant throughout the Oil Creek formation in 
Oklahoma. It is a somewhat variable species, and collection of better or more 
material may see the splitting out of additional species. It is a fact that to 
date no specimens have been collected with both valves together. It is usually 
found as scattered valves in bryozoan debris or in coarse calcarenite, both the 
products of strongly agitated waters. 
ANOMALORTHIS UTAHENSIS Ulrich and Cooper 
Anomalorthis utahensis UtricH and Cooper, Journ. Paleont., vol. 10, No. 7, p. 622, 10936; 
Geol. Soc. Amer. Special Pap. 13, p. 129, pl. 22 C, figs. 11-13, 16, 17, 19-24, 1938. 
Types.—Holotype: 91284; paratypes: 91283a-f ; 91286. 
Horizon and locality—Swan Peak formation in Utah: Smooth Canyon, I 
mile west of Ibex, Confusion Range. Kanosh shale in western Utah. 
Upper Pogonip group in Nevada: On west side Snake Range, 25 miles south 
of Osceola. 
Family DINORTHIDAE Schuchert and Cooper, 1931 
Progessive Orthacea having a subquadrate muscle field in the pedicle valve, 
Orthis-like brachiophores, and a simple cardinal process with crenulated 
myophore. 
Genus DINORTHIS Hall and Clarke, 1892 
Dinorthis Hatt and CLARKE, Pal. New York, vol. 8, pt. I, pp. 195, 222, 1892—-SCHUCHERT 
and Cooper, Mem. Peabody Mus. Nat. Hist., vol. 4, pt. 1, p. 93, 1932. 
DINORTHIS ATAVOIDES Willard 
Plate 57, A, figures 1-11 
Dinorthis atavoides WiLLarD, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, p. 270, 
pl. 2, fig. 4, 1928—Butts, Virginia Geol. Surv. Bull. 52 pt. 2, p. 43, pl. 73, figs. 55-61, 
1942. 
Shell fairly large for the genus, length about one-third less than the width; 
greatest width at about the middle; cardinal extremities obtuse, rounded. Lateral 
margins moderately rounded, anterior margin gently rounded to truncated. An- 
terior commissure gently and broadly uniplicate. Valves unequally convex, the 
brachial valve having the greater depth and convexity. Length of hinge slightly 
exceeding the valve length. Surface marked by 30 to 36 elevated and narrowly 
rounded costae separated by spaces equal to or slightly wider than the costae. 
No bifurcations observed. Median costae largest and widest spaced. 
