PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER gol 
anterior slope are steep. The costellae are differentiated on the posterior and 
median parts but are more nearly equal in size at the anterior. 
Measurements in mm.—117796a, length 27.5, midwidth 28.2, hinge width 33.3, 
height 7.7. 
Described specimens.—117796a,b. 
Horizon and locality—Lenoir formation in Tennessee: 2 miles southeast of 
Whitesburg, Bulls Gap (T.V.A. 171-SE) Quadrangle. 
PIONOMENA Cooper, new genus 
(Greek pion, fat; mene, crescent) 
Shells generally small, attaining a length of about 3 inch; compressed bicon- 
vex; hinge straight, generally not equal to the maximum width which is near 
the middle. Anterior commissure rectimarginate to gently sulcate ; surface multi- 
costellate, costellae varying in size, usually somewhat fasciculate. 
Pedicle interior with moderately large teeth and long, flat dental ridges ; muscle 
area suboval to cordate; posteriorly surrounded by the sides of the delthyrial 
cavity and 2 long, thin, curving plates laid against the inner side of the dental 
ridge. Pseudodeltidium narrowly convex ; foramen small. 
Brachial valve with well-developed chilidium ; cardinal process bilobed, small 
and delicate. Sockets formed by short, wide cups formed by a thin and delicate 
plate. 
Genotype-—Pionomena neumani Cooper, new species. 
Discussion.—This genus is characterized by its biconvex profiles, the fascicu- 
late ornamentation, and the presence of strong dental ridges in the pedicle valve, 
which simulate thin dental plates. The genus differs from Strophomena and 
Rhipidomena in its biconvex profiles, strongly fasciculate ornamentation, and 
the development of thin, curving ridges laid against the inside surface of the 
teeth. 
PIONOMENA ? DUBIA Cooper, new species 
Plate 246, E, figure 15 
Undetermined genus related to Rafinesquina? Burts, Virginia Geol. Surv. Bull. 52, p. 67, 
pl. 80, figs. 1-3, 1942. 
Shells attaining a width of slightly less than an inch; subrectangular in out- 
line, biconvex in profile ; hinge slightly less than the midwidth ; cardinal extremi- 
ties obtuse; anterior margin broadly rounded; surface multicostellate, costellae 
alternating, I or more fine costellae with stronger ones between, about 4 to the 
millimeter at the front margin, all strongly cancellated by strong concentric fila. 
Pedicle valve with lateral profile gently convex and the maximum convexity 
at about the middle; anterior profile broadly convex and with the median region 
subcarinated. Umbo narrowly convex, the convexity continued anteriorly at 
least to the middle as a low, broadening fold; umbonal slopes long and gentle; 
median region swollen; anterior slope long and gentle. Apex perforate. 
Brachial valve gently convex in lateral profile and with the maximum con- 
