PARTI CHAZYAN AND RELATED BRACHIOPODS—COOPER 871 
right angle to alate. Hinge equal to or greater than the width at the middle. 
Lateral margins varying from nearly straight to oblique to greatly rounded. 
Anterior margin narrowly to broadly rounded. Surface ornamented by fine 
radiating costellae of 2 sizes, 1 or 2 costellae separating the larger ones. On the 
lateral slopes, particularly anterior to the cardinal extremities, the costellae be- 
come fairly uniform in size. Finer radii increasing in size toward the anterior 
margin and tending toward uniformity in size along the margin. At the front 
margin of a specimen 33 mm. long, 25 costellae may be counted in 5 mm., but 
in a specimen measuring 46 mm. in length, only 16 costellae were counted in the 
same distance. Entire surface covered by fine concentric fila, about 8 or 9 in a 
millimeter at about the middle, becoming more crowded toward the front. Hinge 
region may or may not be marked by a few oblique wrinkles. 
Adult pedicle valve with posterior half gently swollen and with gentle slopes ; 
anterior half moderately strongly geniculated toward the pedicle valve; genicula- 
tion of lateral portions more gentle. Angle of geniculation between 105° and 
130°. Beak inconspicuous ; foramen small, elongated, often at the anterior of a 
short groove. Interarea moderately long, apsacline. Pseudodeltidium low and 
inconspicuous. 
Posterior half of brachial valve flattened, gently concave at the umbo; anterior 
slope moderately steep; lateral slopes steeper than the anterior one. Umbonal 
region sulcate, sulcus wide and shallow, extending nearly to middle of valve. 
Interior: Muscle area of pedicle valve broadly cordate; diductor scars flabel- 
late, separated by 2 low ridges. Adductor scars elongate elliptical in outline, lo- 
cated somewhat posterior to the middle of the muscle area. Delthyrial chamber 
filled by callus that is extended forward as far as the posterior ends of the adduc- 
tor impressions. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Hypotype\(117683a)). 5 «sseeni ss ae’ 47.0 46.0 59.6 3 78 
ss COS2B2DD ini: 9 cic aie wee a's 52.2 51.7 58.3 63.4 ? 
a CUBS), si8ie nglorsieaasatnse 40.8 39.8 46.0 49.0 6.7 
- (OBAUAA Ys wravcie ncislate oars 33.2 32.0 35.7 38.5 7.0 
. CTIVOOAA coins siaisicisisuisis © 27.2 26.8 28.2 20.3 3.7 
f Cu 760Ha its 24 Massed a 37.8 37.0 44.0 41.2 7.5 
ni CRLF OOAT ae edie «a eertaeaty 18.9 18.1 21.0 21.0 2.3 
Types——Figured hypotypes: 117682a, 117683a, 117684a, 117685, 117686, 
117687, 117688, 117691a, 117692a, 117694a,b; measured hypotypes: 98202a,b, 
1176948. 
Horizon and locality—Benbolt formation in Tennessee: In road cuts 0.9 and 
1.6 miles northeast of Heiskell, Powell Station (T.V.A. 137-SE) Quadrangle; 
3 mile southwest of Mount Eager Church, Hogskin Valley, Powder Springs 
(T.V.A. 154-SW) Quadrangle; Liberty Hill, north of Luttrell, Dutch Valley 
(T.V.A. 154-SE) Quadrangle; 0.1 to 0.2 mile north of the road, 1.1 miles north- 
east of Lee Valley, Lee Valley (T.V.A. 171-NW) Quadrangle; 30 feet above the 
marble on the road along Little Sycamore Creek, 4 mile northeast of the west 
