PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 435 
Measurements in mm.—Holotype, length 15.8, brachial length 16.2, width 21.0, 
hinge width 22.2, thickness 6.0. 
Types.—Holotype: 116996a ; figured paratype: 116996b. 
Horizon and locality—Bromide formation (Mountain Lake member—just 
above bryozoan bed=Mimeila zone) in Oklahoma: On Oklahoma Highway gg, 
3 miles south of Fittstown, Pontotoc County. 
Discussion.—This is apparently a rare fossil because only two specimens have 
been found in all the years of collecting in Oklahoma. It is chiefly characterized 
by the coarse costellae which are stronger than those of any other species of this 
genus for a shell of medium size. In form the species suggests C. superlata from 
Georgia but differs in its stronger costellae and the distinct but broad uniplicate 
anterior commissure. 
CHAULISTOMELLA ELONGATA (Willard) 
Plate 65, D, figures 18-20 
Plaesiomys elongata WitiarpD, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, p. 267, 
pl. 1, figs. 15, 16, 1928, 
This is a rare species, and only a few specimens in all the collections of the 
National Museum and the Geological Survey are referred to it. The figured 
specimen has a somewhat more concave pedicle valve and a less convex brachial 
valve than the type specimen, but the outline and ornamentation agree fairly well. 
Types.—Figured hypotypes: 110473a,b. 
Horizon and locality—Benbolt part of Dryden formation in Tennessee: At 
Liberty Hill, north of Luttrell, Dutch Valley (T.V.A. 154-SE) Quadrangle; 
100 yards west of the store at the juncture of Tennessee Highway 33 and the 
Flint Creek road, Maynardville (T.V.A. 145-SE) Quadrangle. 
CHAULISTOMELLA INAEQUISTRIATA Cooper, new species 
Plate 65, A, figures 1-6; plate 68, C, figures 13-20; plate 69, C, figures 17-21; 
plate 60, D, figure 22; plate 72, B, figures 6-13 
Multicostella cf. M. platys (Billings) Butts, Virginia Geol. Surv. Bull. 52, pl. 90, figs. 37-48, 
1942, 
Shell of about usual size for the genus; wider than long ; widest part at hinge, 
but in some the hinge is narrower than the midwidth; cardinal extremities gen- 
erally acutely angular, often subalate, occasionally obtuse. Lateral margins con- 
cave just anterior to the cardinal extremities but nearly straight to sloping medi- 
ally anterior to the middle, but occasionally broadly rounded. Anterior margin 
nearly straight to gently rounded. Anterior commissure varying from faintly 
unisulcate to slightly uniplicate but generally rectimarginate. Lateral profile 
varying from convexi-concave to convexiplane in the adults and generally un- 
equally biconvex in the young forms. Surface multicostellate, costellae appear- 
ing by implantation in 5 generations, and varying between 9 to I5 in 5 mm. at 
the front. A few specimens show strong fasciculation of the costellae about the 
ribs of the first generation. 
