PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 315 
Types.—Holotype: 116875b; figured paratypes: 116875a,c-e; unfigured para- 
type: 116875f-n. 
Horizon and locality —Lower third of the Pratt Ferry formation in Alabama: 
0.2 mile southeast of Pratt Ferry, Blocton (15’) Quadrangle. 
Discussion.—This species is characterized by its thin, elevated costae, strongly 
inflated pedicle valve and the implantation of a generation of costae on the an- 
terior side of the umbo. It is close to O. bellus from the Chatham Hill of 
Virginia but is more finely and numerously costate and has a much more inflated 
pedicle valve. 
Genus NOTHORTHIS Ulrich and Cooper, 1938 
Nothorthis Utricu and Cooper, Geol. Soc. Amer. Special Pap. 13, p. 106, 1938. 
NOTHORTHIS DELICATULA Ulrich and Cooper 
Plate 38, D, figures 21-29 
Nothorthis celicatula UtricuH and Cooper, Geol. Soc. Amer. Special Pap. 13, p. 106, pl. 17, C, 
figs. 6-14, 1938. 
The figures of this species are introduced for comparison with N. tarda from 
the Pratt Ferry formation of Alabama. 
Types.—Lectotype: G.S.C. 9067e; paratypes: G.S.C. 9067, 9067a-d,f,g. 
Horizon and locality—Upper Canadian or younger, possibly an erratic in the 
lower part of the Lévis shale, Lévis, Quebec. 
NOTHORTHIS TARDA Cooper, new species 
Plate 38, B, figures 3-15 
Shell small, subrectangular in outline; wider than long, with the hinge nar- 
rower than the midwidth; sides gently rounded ; anterior margin gently rounded ; 
anterior commissure gently sulcate; shell multicostellate, costellae increasing by 
intercalation in 3 generations, and numbering about 40, with 4 or 5 in a milli- 
meter at the front margin. 
Pedicle valve deep but having a moderately convex lateral profile with the 
maximum curvature just posterior to the middle; anterior profile narrowly 
domed. Umbo swollen and protruding beyond the posterior margin; median 
region from umbo to anterior margin somewhat narrowly swollen to form a low, 
rounded fold; flanks with steep slopes to lateral margin. Anterior slope gentle. 
Interarea short, curved, apsacline. Teeth small; delthyrial cavity deep but with 
small, short, slightly thickened muscle field ; dental plates, short, thick, receding. 
Vascula media strong, narrow, widely divergent. 
Brachial valve not so deep as the pedicle valve, fairly strongly convex and 
with the maximum convexity at about the middle; anterior profile bilobed with 
the center sulcate and the sides moderately domed; sulcus originating at the 
umbo, widening and deepening to the anterior margin where it occupies some- 
what more than a quarter of the width. Flanks bounding sulcus moderately in- 
flated but with short steep sides. Interior with thick notothyrial platform, nar- 
