PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 439 
Discussion—Chaulistomella magna (Schuchert and Cooper) is one of the 
largest and most robust of described forms. It is further characterized by its 
unequal costellation, its somewhat swollen pedicle valve, and its rectangular form. 
It is very close to C. mitens from which it differs in its larger size, more unequal 
costellae, and less strong sulcus. It is also suggestive of C. mira but differs in 
having a more pronounced fold and sulcus and strongly differentiated costellae. 
CHAULISTOMELLA MIRA Cooper, new species 
Plate 61, D, figures 16-22 
Shell large for the genus, length five-sixths the width; hinge narrower than 
the greatest shell width which is slightly anterior to the middle; sides broadly 
rounded; anterior margin broadly rounded; anterior commissure gently and 
broadly uniplicate; lateral commissure with posterior strongly deflected toward 
the brachial valve ; surface multicostellate ; costellae fairly uniform in size, sepa- 
rated by very narrow striae; costellae numbering from 10 to 15 in 5 mm. at the 
front margin. 
Pedicle valve uneven in lateral profile, the posterior third nearly flat and the 
anterior two-thirds flat to gently concave; anterior profile nearly a straight line 
to very slightly concave ; umbonal region gently swollen; fold obsolete; anterior 
two-thirds and lateral areas flat or barely concave; posterolateral extremities 
gently rounded and deflected. Interarea strongly apsacline ; muscle field bilobate, 
deeply impressed ; pallial marks not well developed. 
Brachial valve strongly convex in lateral profile; strongly convex in anterior 
profile and with long, steep lateral slopes; umbo swollen but without a median 
depression ; median region strongly swollen and with steep lateral slopes; an- 
terior slope long and not so steep as the lateral ones. Umbonal slopes steep to 
the reflected posterolateral extremities. Brachial interior as usual for the genus. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Pralotyye Ware dood. ¢ 2oary 29.0 20.3 36.3 30.5 III 
Paratype (pedicle valve 11700Ic).. 28.3 ? 34.2 30.0 4.4 
4 (brachial valve 117001d). ? 16.9 31.9 27.1 ? 
Types.—Holotype: 117001a; figured paratypes: 11700Ic,d; unfigured para- 
type: I17001b. 
Horizon and locality—Bromide formation (Mountain Lake member- cystid 
bed) in Oklahoma: At the first dam on Spring Creek, N4 sec. 17, T.2S., R. 1 
W., Murray County. 
Discussion.—This species is characterized by its large size, fairly even costellae, 
and poor development of fold and sulcus. The species is a large and robust one 
like C. magna (Schuchert and Cooper) but differs in its subdued fold and sul- 
cus, fairly uniform costellae, and the lesser development of pallial impressions. 
It is a larger species than C. nitens which, however, has a well-defined fold and 
sulcus. 
