PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 443 
Brachial valve strongly convex in lateral profile with the anterior slope flat- 
tened but steep ; anterior profile strongly convex with steep lateral slopes ; median 
region and umbo swollen; sulcus shallow and narrow, extending from umbo to 
anterior margin but indistinct in the anterior third; lateral and anterior slopes 
steep ; interarea short, steeply apsacline. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
ELGIOLYDE Ses cR ess Seats 18.1 18.2 23.7 25.2 9.0 
Paratype (117005a) ........ 17.9 18.5 24.9 24.3 10.8 
Types——Holotype: 117006; figured paratype: 117005a. 
Horizon and locality—Wardell formation (Hesperorthis—Camerella beds), 
Evans Ferry section in Tennessee: On U. S. Highway 25E, 4 mile north of 
Indian Creek, Howard Quarter (T.V.A. 162-NW) Quadrangle; also just above 
Hesperorthis at same locality as preceding; north side of the road, 1.1 miles 
northeast of Lee Valley, Lee Valley (T.V.A. 171-NW) Quadrangle. 
Discussion.—The species is characterized by its rectangular outline, flattish 
pedicle valve, and strongly convex brachial valve. It resembles C. lebanonensis 
in form and proportions but has a less concave pedicle valve and a much more 
convex brachial valve. Its compact and strong form separate it from C. superlata. 
CHAULISTOMELLA RIDLEYENSIS Cooper, new species 
Plate 64, A, figures 1-5; plate 67, A, figures 1-7 
Small for the genus, subquadrate in outline, wider than long with the hinge 
forming the widest part or slightly narrower than the midwidth; sides concave 
just anterior to the cardinal extremities, sloping slightly medianly near the mid- 
dle; anterolateral extremities somewhat narrowly rounded; anterior margin 
broadly rounded; anterior commissure uniplicate; surface multicostellate, cos- 
tellae narrowly rounded, separated by spaces at least equal in width to the cos- 
tellae; about 9 costellae in 5 mm. at the anterior margin of the brachial valve. 
Pedicle valve with variable lateral profile; posterior third moderately convex 
but anterior two-thirds flat to gently concave; umbonal region slightly swollen; 
median region flat to concave; lateral areas flat to gently swollen; posterolateral 
extremities deflected more or less strongly in the direction of the brachial valve ; 
interarea long, strongly apsacline. Muscle field fairly deeply indented anteriorly 
and with moderately large adjustor scars. 
Brachial valve moderately convex in lateral profile; strongly convex in an- 
terior profile with short and steeply sloping sides; median and anterior regions 
strongly swollen; sulcus originating on the somewhat swollen umbo, extending 
to the middle but indistinct on the anterior ; umbonal slopes short and steep. In- 
terior with short brachiophores, moderately thick notothyrial platform, and large 
erect cardinal process. 
