704 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
not so strongly alate, and the bands of fine costellae are much narrower. The 
species is suggestive of S. varicostellata but is a larger species. 
SOWERBYELLA SILICICA NANA Cooper, new subspecies 
Plate 196, C, figures 15-19 
Sowerbyella sp. Butts, Virginia Geol. Surv. Bull. 52, pt. 2, p. 42, pl. 73, fig. 38, 1942. 
Shell small, wider than long with the width about one-third greater than the 
length; hinge forming widest portion; cardinal extremities forming an acute 
angle; slightly auriculate. Lateral margins slightly indented just anterior to the 
cardinal extremity and nearly straight or slightly curved before joining the 
narrowly rounded anterior margin. In old specimens the anterior commissure 
is sulcate and the anterior margin may be slightly produced by the sulcus. Sur- 
face marked by costellae of unequal size, about 28 of the larger costellae sepa- 
rated by 2 to 4 of the finer ones. 
Pedicle valve having a gently convex lateral profile but with the anterior pro- 
file strongly arched at the middle and with sides flattened. Beak low, inconspicu- 
ous, scarcely protruding posterior to the posterior margin. Umbonal region nar- 
rowly swollen and produced forward to join with a conspicuous, rounded, but 
low fold. Lateral slopes flattened, moderately steep. On each side of the fold a 
low plica is often visible on the lateral slope and extending to the anterolateral 
extremity. Interarea nearly flat, moderately to strongly apsacline. Pseudodel- 
tidium short, narrow. 
Brachial valve unevenly concave with the greatest concavity located along the 
median line where the valve is deeply sulcate. Umbo concave. Flanks of shell 
bounding sulcus only moderately concave and with 2 indefinite but perceptible 
plicae corresponding to the depressed areas of the ventral flanks bounding 
the fold. Interarea anacline. 
Interior: Nothing known beyond the presence of the 2 diverging septa. 
Measurements in mm.— Buen Hinge 
Length length Midwidth width Thickness Height 
HIGloty Be Voss sis sec tle» we 6.4 6.1 8.2 8.0 1.4 21 
Paratype (117518a)..... 6.6 5.9 8.3 9.4 1.8 2.3 
* (GiB) hoaor 6.7 5.9 8.4 9.0 1.4 2.6 
oe (2175186) ence 6.2 5.3 8.6 8.7? Lz 2.2 
Types.—Holotype: 98229a; unfigured paratypes: 98229b, 117518a-c. 
Horizon and locality.—Arline formation in Virginia: At entrance to Porter- 
field Quarry, 5 miles east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle. 
Discussion.—This subspecies differs from S. silicica in its somewhat smaller 
size and in the nearly rectangular cardinal extremities. 
SOWERBYELLA SOCIALIS Cooper, new species 
Plate 108, B, figures 23-44; plate 205, A, figures 1-6 
Sowerbyella sp. Butrs, Virginia Geol. Surv. Bull. 52, pt. 2, p. 93, pl. 90, figs. 1-16, 1942. 
Shell semielliptical, length about two-thirds the width at the middle; hinge 
forming widest part ; cardinal extremities acute, often drawn out into small ears; 
