PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 423 
from the median region. Interarea slightly longer than the brachial one, curved, 
apsacline. 
Brachial valve unevenly convex in lateral profile with a convex umbo but 
gently convex midregion and anterior region. Sulcus deepest in the posterior 
half, disappearing at about three-fourths the length from the beak. Flanks moder- 
ately swollen. Slopes to cardinal extremities moderately steep. 
Interior with pedicle muscle field short and narrow. Diductor scars not widely 
divergent. Brachial valve having a small cardinal process. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
FIGOLV DE te cles sesenee 14.0 13.8 15.8 13.7 6.5 
Paratype (troqo3d)\...... 2. 15.4 14.5 16.4 13.0 7.9 
% (rreqo2gy "Ss... 14.3 14.1 17.2 10.7 ? 6.9 
ii CrrodoZztyn vr. os ES 15.3 14.4 16.1 12.8 6.9 
Types.—Holotype: 110403e; figured paratypes: 110403b-d; unfigured para- 
types: 110402a-e, 110403a,f; measured paratypes: 110402f,g. 
Horizon and locality——Arline formation in Tennessee: North side of wagon 
road in glade, + mile southeast of Friendsville, Concord (T.V.A. 138-SW) 
Quadrangle. 
Discussion.—This species is characterized by its small size (it and M. fascicu- 
lata Butts are the smallest known species), its relatively strong convexity, par- 
ticularly of the brachial valve, rounded outline, and narrow hinge. In these re- 
spects it differs from known species. 
MULTICOSTELLA PLICATA Cooper, new species 
Plate 63, D, figures 22-29 
Large for the genus, somewhat variable; wider than long with the greatest 
width at the hinge in well-preserved specimens; sides nearly straight or gently 
rounded; anterior margin broadly rounded; anterior commissure varying from 
slightly uniplicate to slightly sulcate ; lateral commissure slightly deflected toward 
the brachial valve at the cardinal extremities; brachial valve having a slightly 
deeper profile than the pedicle one; cardinal extremities varying from slightly 
acute to slightly obtuse, occasionally slightly auriculate; surface multicostellate, 
costellae narrow, elevated, about equal in width to the spaces between them ; about 
8 costellae in 5 mm. at the front margin of a specimen 21 mm. long; costellae pro- 
duced in several generations ; costellae crossed by strong elevated fila. 
Pedicle valve unevenly convex in lateral profile, most convex in posterior half 
but convexity very low; anterior half gently convex ; anterior profile broadly but 
slightly convex ; umbo narrowly convex, the convexity continued anteriorly as a 
low fold perceptible in most specimens to the front margin, in a few fairly con- 
spicuous; flanks bounding sulcus depressed convex; posterolateral extremities 
deflected more or less strongly toward the brachial valve. Interarea moderately 
long, strongly apsacline. Interior with short dental plates and shallow umbonal 
