PART I CHAZYAN AND RELATED BRACHIOPODS—-COOPER 419 
Shell of about median size for the genus; wider than long with the hinge nar- 
rower than the midwidth; sides rounded; anterior margin broadly rounded ; an- 
terior commissure rectimarginate ; valves subequally convex; surface unequally 
costellate, the strong costellae scattered among the finer ones; about 3 costellae 
to the millimeter at the anterior margin. 
Pedicle valve unevenly convex in lateral profile, the posterior half gently con- 
vex but the anterior half flattened; anterior profile with the median region nar- 
rowly folded with long, gentle and flat slopes to the margins; umbo narrowly 
swollen, the swelling continued anteriorly for about half the length as a low 
fold; flanks bounding fold depressed slightly and with gentle slopes to the ex- 
tremities. Interarea moderately long, apsacline. 
Brachial valve with a gently convex lateral profile; anterior profile broadly 
but gently convex and with the median region narrowly depressed ; umbo sulcate, 
sulcus narrow and shallow, extending to about the middle where it becomes 
shallower and wider, nearly to disappear at the front margin; flanks bounding the 
sulcus somewhat swollen; posterolateral slopes long and gentle; interarea short 
and gently anacline. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotyperid as. est nihews omonrs } 9.7 9.0 11.6 11.6 4.2 
Hypotype (116987) .......... 13.5-+ 13.0 17.2 iy 5.9 
Types.—Holotype: 71493; figured hypotype: 116987. 
Horizon and locality.—Little Oak formation in Alabama: On U. S. Highway 
31, 4 mile north of Pelham, 660 feet east of the intersection of main Cahaba Val- 
ley road with Helena road, Bessemer Iron District (15’) Quadrangle; junction 
of Bailey Gap and Cahaba Valley roads, 13 miles northeast of Newhope Church, 
SWiSW3 sec. 13, T. 19 S., R. 2 W., Vandiver (15’) Quadrangle. 
Discussion.—In size and form this species suggests M. robusta, but it is much 
more strongly costellate and the costellae are strongly fasciculate. It is possible 
that the specimens of this species so far available are in reality only young ones. 
MULTICOSTELLA GERONTICA Cooper, new species 
Plate 62, C, figures 15-20 
Shell large, subquadrate in outline with the width greater than the length; 
cardinal extremities acutely angular, subauriculate. Valves subequal in depth and 
convexity, the brachial valve having slightly more depth than the pedicle valve. 
Lateral margins concave just anterior to the cardinal extremities or obliquely 
straight ; anterior margin broadly rounded. Anterior commissure rectimarginate. 
Surface multicostellate, with 7 to 10 costellae in 5 mm. at the front of an adult. 
Pedicle valve with the most convex part in the umbonal region, flattened an- 
teriorly. Fold obsolete anterior to the posterior third. Anterior half and flanks 
very gently convex ; slopes to cardinal extremities very gentle. Beak fairly large, 
protruding beyond the posterior margin. Interarea moderately long, curved, 
apsacline. 
