PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 521 
about 7 in the space of 5 mm. at the front margin; a few costellae may be larger 
than the surrounding ones. 
Pedicle valve hemiconical in lateral profile; anterior profile broadly triangular. 
Median region somewhat swollen; lateral areas with long, moderately steep 
slopes; interarea catacline, long; plates bounding delthyrium moderately high. 
Spondylium wide and shallow ; median septum moderately long. 
Brachial valve nearly flat to gently convex in lateral profile; same in anterior 
profile; umbo sulcate; sulcus shallow, widening to the front margin. Flanks 
bounding sulcus gently swollen; cardinal extremities deflected slightly toward 
the pedicle valve; chilidium small; notothyrial platform thick, cardinal process 
thin ; median ridge reaching the middle ; pallial marks moderately well developed. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype (pedicle valve) .......... 15.3 ? 22.0 23.5 5.8 
Paratype (brachial valve 117012a).. ? 15.7 22.3 20.3 3.4? 
Types——Holotype: 117012d; figured paratypes: 117012a-c,e,f,i; unfigured 
paratypes : 117012g,h,j. 
Horizon and locality.—Lincolnshire formation (Hogskin member) in Tennes- 
see: 0.4 mile east-northeast of Red Hill, 4 miles west-southwest of Thorn Hill, 
Avondale (T.V.A. 162-SW) Quadrangle; Republic Marble Quarry near Lut- 
trell; south side of the school just north of the railroad crossing at Chesney, 
Luttrell (T.V.A. 155-NW) Quadrangle. 
Discussion.—This is not a common species. It is suggestive of dA. perfectum 
in its ornamentation but differs in its proportions ; it is a much wider shell with 
a flatter brachial valve. None of the localities has yet yielded a specimen with 
both valves in contact. 
ATELELASMA OKLAHOMENSE Cooper, new species 
Plate 80, C, figures 12-19 
Of about medium size for the genus, wider than long, with acute cardinal ex- 
tremities and the hinge forming the widest part. Pedicle valve hemipyramidal 
with a broad, flat, and procline interarea. Beak pointed and slightly upturned. 
Brachial valve nearly flat with posterior portion extending well beyond the 
pedicle interarea, exposing the cardinalia to view. Surface marked by strong 
costellae separated by furrows narrower than the costellae. Costellae crossed by 
strong concentric fila. About 9 costellae in the space of 9 mm. at the front margin. 
Margin of delthyrium bordered by low plates set obliquely on the delthyrial 
edge and decreasing to disappearance toward the beak. Spondylium fairly short. 
Chilidium short and appearing as a broad arch over a thin cardinal process. 
Measurements in mm.—Holotype, length 10.8, hinge width 16.3, length of 
pedicle valve 8.9. 
Types.—Holotype: 110124; figured paratype: 110125. 
Horizon and locality —Bromide formation (Mountain Lake member—near top 
