PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 295 
Measurements in mm.—Holotype, length 15.2, width 18.2, hinge width 21.4, 
thickness 4.1. 
Type.—Holotype: 109797. 
Horizon and locality—Probably Arline formation in Tennessee: James Way- 
land Farm near Riverdale, 9 miles east of Knoxville, Shooks Gap (T.V.A. 
147-NE) Quadrangle. 
Discussion.—This is a large species suggestive of O. buttsi but differs from 
that species in its stronger costae and much larger size. 
ORTHAMBONITES BELLUS Cooper, new species 
Plate 35, D, figures 35-51 
Shell small for the genus, slightly wider than long, hinge slightly narrower 
than the greatest shell width which is at the middle. Cardinal extremities approxi- 
mating a right angle. Lateral margins nearly straight ; anterior margin narrowly 
rounded. Surface marked by narrowly rounded costellae separated by interspaces 
slightly narrower than the costellae. Intercalated costae occur, but intercalation 
takes place only in I generation on the umbo or in its vicinity ; 30 to 32 costae at 
the anterior margin. 
Pedicle valve with umbo and posteromedian portion swollen, beak prominent 
and with part of the umbo protruding posterior to the posterior margin. Anterior 
slope moderately steep, lateral slopes moderately steep but more so than the 
anterior one. Interarea moderately long, strongly curved, apsacline. Lateral pro- 
file moderately strongly convex and with the greatest curvature in the posterior 
half. 
Pedicle interior with moderately strong teeth and thick dental plates that con- 
verge slightly toward the floor of the valve. Crural fossettes narrow but deep. 
Muscle area confined to the delthyrial cavity. Posterior portion of pallial trunks 
poorly defined. 
Brachial valve gently convex in lateral profile, very broadly convex in anterior 
profile. Umbonal region moderately swollen. Sulcus originating less than a 
millimeter anterior to the beak, narrow and shallow, not reaching the anterior 
margin in adult shells. Flanks bounding the sulcus moderately convex with long 
gentle posterolateral slopes to the posterolateral extremities which are somewhat 
flattened. 
Brachial interior with moderately long brachiophores, supported by shell sub- 
stance deposited along their lower edge. Sockets moderately deep. Notothyrial 
platform swollen in adults ; cardinal process simple, thickest anteriorly and taper- 
ing posteriorly to a thin septum. Muscle field indistinct. 
Measurements in mm.— 
Length Width ae Thickness 
Paratype (pedicle valve 116866b) ..... 0.7 10.6 09.6 14 
es Comal tio) DE OGOGS))) seers 8.9 10.1 9.9 ? 
r (brachial valve 116866d) .... 9.6 11.8 10.3 ? 
a ris: So (9 1686680 1s. . 2006 T1-7 10.6 ? 
x (both valves 116866g) ....... 10.2 10.6 10.1 4.5 
