PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 441 
CHAULISTOMELLA NITENS Cooper, new species 
Plate 67, C, figures 17-23 
Shell fairly large for the genus, wider than long; hinge about equal to the 
midwidth ; cardinal extremities forming a right angle; sides straight; antero- 
lateral extremities forming a right angle; anterolateral extremities and anterior 
margin broadly rounded; anterior commissure rectimarginate; lateral commis- 
sure deflected toward the brachial valve at its posterior ; surface multicostellate ; 
costellae fairly even in size, separated by narrow interspaces, about 10 costellae 
in 5 mm. at the front margin. 
Pedicle valve unevenly convex in lateral profile with the posterior third flatly 
convex and the anterior two-thirds nearly flat ; anterior profile nearly flat ; umbo 
gently swollen, marked by a poorly defined fold extending to the front margin; 
anterior half depressed ; flanks bounding depressed area faintly convex; postero- 
lateral extremities more or less strongly deflected toward the brachial valve; 
interarea moderately long, nearly catacline; muscle field fairly strongly im- 
pressed, length and width about equal, moderately deeply indented anteriorly ; 
adjustor scars small; diductor scars large; pallial marks lightly impressed. 
Brachial valve fairly evenly and moderately convex in lateral profile; anterior 
profile broadly convex; anterior commissure moderately convex, highest in the 
middle; umbonal, median, and anterior regions fairly strongly swollen; lateral 
slopes moderately long and steep ; umbo sulcate ; sulcus narrow, shallow, extend- 
ing from umbo to anterior margin; interarea moderately long, fairly strongly 
apsacline. Cardinal process stout; median ridge short; notothyrial platform 
moderately thickened. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
FIOLOLY Dey rae 6 Sei ase Mando ah 233 24.2 30.8 30.1 II.0 
Paratype: (117003b)) .....05. «1 22.6 233 29.4 27.6 10.8 
Types.—Holotype: 117003a; figured paratype: 117003c; unfigured paratype: 
117003b. 
Horizon and locality.—Bromide formation (Mountain Lake member) in Okla- 
homa: On the east side of the road cut on Oklahoma Highway 18, 1.8 miles 
south of Sulphur, Murray County. 
Discussion.—This species is recognized by its transverse form and general 
resemblance to C. magna (Schuchert and Cooper). It differs from the latter in 
its smaller size, somewhat more concave pedicle valve and stronger fold and 
sulcus. It is associated with C. mundula but is distinguished by its greater width 
and stronger costellae. 
CHAULISTOMELLA OBESA Cooper, new species 
Plate 67, B, figures 8-16 
Shell moderately large, length equal to about five-sixths of the width. Cardi- 
nal extremities obtusely rounded, strongly deflected toward the brachial valve. 
