PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 787 
SOWERBYELLA NASUTA Cooper, new species 
Plate 199, C, figures 18-34; plate 215, A, figures 1-4 
Shell small, subquadrate, wider than long; sides nearly straight ; cardinal ex- 
tremities nearly a right angle; ears small; anterior margin subnasute. Finely 
costellate, with about 5 or 6 costellae in 1 mm. at the front margin. 
Pedicle valve fairly strongly and evenly convex in lateral profile with the me- 
dian region being the most convex part ; anterior profile broadly convex ; umbonal 
region narrowly convex, often subcarinate medianly, the convexity continued to 
the front margin as a moderately strong, narrow median fold; flanks gently in- 
flated, depressed somewhat below the median fold and with moderately steep 
slopes to the margins. Interarea moderately long, strongly apsacline. Interior 
with short, rounded, deeply impressed diductor scars with strong, branched 
pallial sinuses diverging from their anterior ends. Median ridge low. 
Brachial valve gently concave and marked by a distinct narrow, shallow sul- 
cus extending from beak to anterior margin; flanks bounding sulcus gently con- 
cave to flattened; posterolateral extremities flattened. Interior with 2 closely 
spaced septa strongly elevated near the middle of the valve; slope anterior to 
anterior ends of septa steep, strongly papillose. Sides depressed, papillose, and 
moderately thickened inside the margin. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
| 0) 00) 5,0 en 8.1 7.4 9.9 10.1 253 2.9 
Paratype (117503a)..... 7.0 6.2 8.9 9.2 Ait 2.5 
F CIT7503C)iencr 7.0 6.3 9.0 9.5 2.1 28 
Fr (rT75024a)" 7.2 6.4 5.9 8.3 9.7 1.9 2.3 
Types.—Holotype: 117503b; figured paratypes: 117502a-c, 117503a,c-h; 
figured specimen: 117501. 
Horizon and locality—Chatham Hill formation in Virginia: On the north 
slope of Walker Mountain, 2 miles south-southwest of Chatham Hill, Chatham 
Hill (T.V.A. 218-NE) Quadrangle. 
Ward Cove formation (Nidulites bed) in Virginia: Thompson Valley, south- 
west of Tazewell, Pounding Mill (15’) Quadrangle. 
Ward Cove formation (just above Nidulites) in Virginia: North of U. S. 
Highway 19, 4 mile west of Pounding Mill, Pounding Mill (15’) Quadrangle. 
Discussion.—This little species is characterized by the prominent median fold 
on the pedicle valve. This fold is narrow and extends from the beak to the an- 
terior margin and may cause the margin to become nasute. A number of species 
have developed a median fold similar to this one, but it is not so marked in any 
other species as in this one and S. subcarinata. Sowerbyella nasuta differs 
from S. carinata in size and proportions, the former being more quadrate and 
having a length/width index of about 0.78 whereas that of S. subcarinata aver- 
ages about 0.70. 
