PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 493 
interior with narrow and shallow notothyrial cavity ; brachiophore plates attached 
high on median septum. 
Measurements in mm.—Holotype, length 2.4, brachial length 1.9, midwidth 
3.2, hinge width 3.9, thickness 1.6, 
Types.—Holotype: 117070a; figured paratypes: 117070b-d. 
Horizon and locality—Pratt Ferry formation (lower 3 feet) in Alabama: 0.2 
mile south of Pratt Ferry, Blocton (15’) Quadrangle. 
Discussion.—This species has a deep sulcus and moderately strong fold. The 
brachial valve is fairly deep, and the costae are strong. It differs from S. costatus 
in having a more convex brachial valve with a deeper sulcus. The shape of the 
Alabama species is also considerably different from that of the Virginia form. 
SKENIDIOIDES COSTATUS Cooper, new species 
Plate 97, D, figures 38-48 
Shell of about usual size for the genus, wider than long, with acutely angular 
and slightly auriculate cardinal extremities, gently sloping lateral margins, and 
broadly rounded to truncate anterior margin. Lateral profile planoconvex. Sur- 
face marked by about 19 to 21 strong costellae in the adult. The costellae appear 
in 3 generations. In a young valve 1.5 mm. in length, 13 primary costae are 
present which increase by intercalation to 19 or 21. In all stages of growth the 
median costa is stronger and more elevated than the others and forms a fold. 
Intercalation on each side of median costa takes place about one-third the length 
from the beak. 
Pedicle valve evenly and strongly convex in lateral profile with the greatest con- 
vexity located at about the middle; in anterior profile this valve is subcarinate 
and the central costa is slightly elevated above those forming the flanks. Flanks 
flat in profile and moderately steep. Interarea long, slightly curved near the beak, 
and strongly apsacline. 
Brachial valve flat in anterior profile. Umbo slightly convex, but just anterior 
to it a narrow sulcus forms which deepens and widens rapidly anteriorly to oc- 
cupy about half the width of the valve at the front. Seven costae occupy the 
sulcus. Shell surface between the costae bounding the sulcus and the cardinal 
extremities perceptibly but only slightly concave. 
Interior: Pedicle valve with long, slender teeth and short, shallow free 
spondylium. Median septum of brachial valve moderately thick and greatly ele- 
vated, so that the valve is separated into two parts. Notothyrial cavity shallow 
and narrow ; brachiophores long and slender. 
Measurements in mm.— 
Hinge 
Length Width width Thickness 
Fidlotype sree oh. iteee tis ogetd dooreens 3.0 4.2 4.9 17) 
IPE elgg sa Willy. o 270) ee eee 1.5 3.0 37, 0.7 
Types.——Holotype: 117072f; figured paratypes : 117072a-c,i,j ; unfigured para- 
types: 117072d,e,g,h. 
