PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 625 
Highway 74 and U. S. Highway 61 at Rock Levee, 34 miles southwest of Cape 
Girardeau, NW. corner sec. 24, T. 30 N., R. 13 E., Cape Girardeau (15’) 
Quadrangle. 
Discussion ——This species may be recognized by its strong costae and by the 
slight development of the fold and sulcus, in which respect it differs from 
A. crassa. 
ANCISTRORHYNCHA ? PERPLEXA Cooper, new species 
Plate 127, C, figures 14-19 
Shell small for the genus, subcircular in outline; apical angle about 115°; 
sides narrowly rounded; anterior margin truncated. Anterior commissure 
strongly uniplicate. Surface costate, more strongly than usual in the genus, costae 
narrowly rounded with deep separating grooves; 4 costae on the fold, 3 in the 
sulcus, and 7 or 8 on the flanks. 
Pedicle valve fairly strongly convex in lateral profile and with the greatest 
convexity at the middle; anterior profile moderately and broadly convex ; umbo 
narrowly swollen ; median region swollen ; sulcus originating at about the middle, 
moderately deep, occupying slightly less than half the midwidth; tongue moder- 
ately long; flanks somewhat inflated and with moderately steep slopes. Beak 
long and strongly incurved. 
Brachial valve slightly deeper than the pedicle valve, strongly convex in both 
profiles ; umbo flattened and sulcate; sulcus short, shallow, and disappearing at 
the middle where the fold originates ; fold short and low; flanks swollen and with 
steep lateral slopes. 
Measurements in mm.—Holotype, length 6.0, brachial length 5.5, width 6.4, 
thickness 4.5. 
Type.—Holotype: 111297. 
Horizon and locality—McLish formation in Oklahoma: In sec. 35, T. 1 S., 
R. 7 E., 1 mile southwest of McLish Ranch house, west of Bromide, Johnston 
County. 
Discussion—This species is characterized by its sharp and strong costae, the 
moderately deep sulcus, and sharply defined fold. These features, not usually 
seen in Ancistrorhyncha, distinguish it from all known species of the genus. A 
median septum was not observed in the brachial valve, the presence of which 
could relate the species to Rostricellula or allied forms. This species is therefore 
tentatively placed in Ancistrorhyncha. 
ANCISTRORHYNCHA ? VACUA Cooper, new species 
Plate 128, C, figures 10-13 
Shell small, subtriangular to subpentagonal in outline. Posterolateral margins 
straight forming an angle of go° at the beak. Sides narrowly rounded and with 
the greatest shell width located slightly anterior to the middle. Anterior margin 
broadly rounded. Anterior and lateral margins faintly costate, posterior half (?) 
