PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 643 
forming an apical angle of about 82°. Anterolateral extremities narrowly 
rounded; anterior margin gently curved. Sulcus marked by 4 to 5 costae, the 
fold by 5 to 6 costae, and the flanks by 5 or 6 costae. Surface crossed by mod- 
erately strong fila. 
Pedicle valve fairly evenly but gently convex in lateral profile; anterior profile 
gently depressed in the median region, precipitous on the sides. Beak narrow, 
incurved ; umbo slightly swollen ; sulcus originating about 7 mm. anterior to the 
beak; sulcus shallow and broad, occupying about half the width. Sulcus de- 
pressed slightly below the flanks at the front; flanks narrow, rounded, and steep. 
Brachial valve deeper than the pedicle valve, moderately convex in lateral 
profile and with the umbonal region having the greatest curvature; anterior pro- 
file moderately arched. Fold broad and low, not strongly elevated at the front, 
and its place of origin not clear but near the middle; flanks strongly rounded 
and precipitous. 
Measurements in mm.— 
Brachial 
Length length Width Thickness 
HiGloty pes... 2A? SVT. - 14.2 12.8 13.8 8.7 
Paratype stash besos oS) Bent . <3 14.4 13.1 12.8 8.9 
Types.—Holotype: 117222; figured paratype: 111532. 
Horizon and locality—Dryden formation (=Wardell part) in Virginia: In 
a quarry just east of Virginia State Highway 70, north of Powell River, 1.6 
miles south of Jonesville, Ben Hur (T.V.A. 170-NE) Quadrangle. 
Same formation in Tennessee: At Mulberry Gap in Powell Mountain, 5 miles 
north of Sneedville, Sneedville (T.V.A. 170-SW) Quadrangle. 
Hostler formation in Pennsylvania: At the National Lime Quarry, Shrader 
Station= Naginey Post Office, Lewistown (15’) Quadrangle. 
Ooltewah formation in Tennessee: 34 miles north of Ooltewah, Ooltewah 
(T.V.A. 112-SE) Quadrangle. 
Discussion.—This species is characterized by having its length and width 
nearly equal but with the length often the greater, a low, wide fold, and sulcus 
marked by numerous costae. The species is very similar to R. plena of the Val- 
cour limestone, New York, but does not attain the large size and robust form of 
that species. Rostricellula plena usually has deeper valves, with a more incurved 
pedicle beak and more numerous costae on the fold and in the sulcus. Rostricel- 
lula ovata differs from R. rostrata in its more elongate form and the fact that the 
greatest width is more anterior than that of FR. rostrata. Furthermore, the fold 
of the latter species is more pronounced and the costae less numerous and more 
distant in R. rostrata. 
ROSTRICELLULA PARVA Cooper, new species 
Plate 134, C, figures 27-32 
Shell small, triangular in outline, slightly wider than long; greatest width at 
about the middle; anterior margin nearly straight; apical angle slightly greater 
