PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 525 
Flanks bounding sulcus swollen; posterolateral slopes short and steep. Median 
ridge long ; notothyrial platform moderately wide. 
Measurements in mm.—Holotype, length 13.5, brachial length 14.3, width 18.8, 
hinge width 20.7, thickness 9.0. 
Types.—Holotype: 117013. 
Horizon and locality—Tulip Creek formation in Carter County, Okla.: 152 
feet above the top of the basal sand on the first creek east of U.S. Highway 77, 
SELNE4NES sec. 25, T. 2 S., R. 1 E., Carter County; 3 miles north-northeast 
Gt oprmeer, SE4 sec. 32, IT. 2 5., R28, 
Discussion—This is a very rare species; three specimens only have been 
found. One complete, beautifully preserved specimen furnished the details of 
the exterior. Two poorly preserved specimens showing the interior of both 
valves yielded some idea of the interior. The species is characterized by large size, 
rectangular outline, somewhat compressed form, convex brachial valve, and 
fairly strong median sulcus. It differs from A. perfectwm in its proportions which 
are more widely rectangular than subquadrate. It differs from A. obscurum in 
the details of its ornamentation, which is much finer, and in its more convex 
brachial valve. It is quite unlike A. oklahomense in outline, profile, and orna- 
mentation. 
ATELELASMA VARIABILE Cooper, new species 
Plate 81, A, figures 1-6; plate 82, K, figures 43-47; plate 82, L, figures 48-52 
Shell small for the genus, variable in outline, wider than long, nearly square 
in large specimens with the hinge slightly wider than the midwidth; sides slop- 
ing gently toward the middle ; anterior margin varying from broadly rounded to 
gently emarginate. Anterior commissure rectimarginate. Costellae variable, 
crowded, and separated by spaces narrower than the width of the costellae; 2 
to 3 costellae occupy the space of 1 mm. at the anterior margin. 
Pedicle valve gently convex in lateral profile ; anterior profile broadly triangu- 
lar ; median region somewhat flattened ; lateral areas somewhat rounded ; postero- 
lateral extremities deflected toward the brachial valve. Interarea long, strongly 
apsacline to catacline. 
Brachial valve faintly convex to flat in lateral profile; anterior profile very 
slightly convex ; umbo sulcate; sulcus shallow, widening anteriorly to the front 
margin, deepest in the median region and becoming shallower at the front mar- 
gin. Flanks bounding sulcus moderately swollen; posterolateral extremities 
depressed. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holoty petites Eeok. 6.8 7 fe} 0.7 9.9 5.0 
Paratype (1170I5b).... 9.7 9.7 11.7 ? 6.0 
cs (7I7pEse)y. 3, 5.0 6.3 8.5 ? 3.8 
Types.—Holotype: 117015; figured paratype: 117015c; unfigured paratypes: 
117015a,b; figured specimen: 117996. 
