788 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
SOWERBYELLA NEGRITUS (Willard) 
Plate 197, A, figures I-10 
Plectambonites negritus WiLtLarp, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, 
p. 278, pl. 3, fig. 13, 1928. 
Sowerbyella sp. Butts, Virginia Geol. Surv. Bull. 52, pt. 2, p. 72, pl. 81, figs. 21, 22, 1942. 
Shell of about medium size for the genus, wider than long with the length 
about two-thirds the width; hinge forming the greatest width and about twice 
the length. Lateral margins slightly curved; anterior margin broadly rounded. 
Surface marked by costellae of unequal size. Five to seven of the stronger cos- 
tellae may be counted on each side of a still stronger median costella. The 
stronger costellae define low plications that wrinkle the front margin. Between 
the stronger costellae 2 to 8 of the finer radii occur. About 13 costellae may be 
counted in 2 mm. at the front of a large valve. In addition to the costellae 4 
oblique wrinkles are present along the hinge on each side of the beak. 
Pedicle valve evenly and moderately convex in lateral profile and with the 
most convex part of the shell at the middle. Anterior profile with sides rising 
gradually to the highest part in the middle of the valve which is humped into a 
low fold. Beak inconspicuous and only slightly produced posterior to the pos- 
terior margin. Beak and umbo produced into a low fold broadening anteriorly 
to occupy about one-quarter of the width. Region about cardinal extremities 
flattened, rising gradually to the base of the fold. Sides of fold moderately steep. 
Interarea short, nearly flat, apsacline. 
Brachial valve strongly concave with the greatest concavity in the median 
region. Sulcus narrow and extending to the anterior margin where it indents 
the commissure toward the pedicle valve. Concavity decreasing laterally. Cardi- 
nal extremities sulcate, deflected toward the pedicle valve. Anterolateral areas 
not strongly incurved. 
Interiors: Not known in detail. Structures of brachial valve appear to be 
characteristic of Sowerbyella. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
Hypotype (117504a)... 6.1 5.3 9.7 II.9 1.3 1.8 
ff (117504c)... 5.8 ? 8.8 10.8 ‘4 2.0? 
ss (117506a)... 7.8 ? 13.0 15.0 ? ? 
Types.—Holotype: M.C.Z. 8615; figured hypotypes: 117504a,c, 117505d, 
117506a,b. 
Horizon and locality—Botetourt formation in Virginia: At junction of Vir- 
ginia Highways 311 and 114, 4 mile southwest of Catawba, 11 miles north of 
Salem, Salem (15’) Quadrangle; 14 miles southeast of Harrisonburg, Harrison- 
burg (15’) Quadrangle; on Virginia Highway 114, 2.3 miles west of Mont- 
gomery-Roanoke County line, 12 miles northeast of Blacksburg. 
Effna formation in Virginia: At Porterfield Quarry, 5 miles east of Saltville, 
Maccrady (T.V.A. 218-NW) Quadrangle; McNutt Quarry, 12 miles southwest 
of Bland, Burkes Garden (15’) Quadrangle. . 
