796 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
paratypes: 98206a-d, 98027a,c-e, 117519a,b, 117520a,b, 117521, 117523b, 
117524b, 117525c, 117527b. 
Horizon and locality—Wardell formation and Wardell part of Dryden forma- 
tion in Clinchport (T.V.A. 188-NW) Quadrangle, Virginia: At Lloyd Carter’s 
barn, 0.8 mile northeast of the new school at Rye Cove; several other localities 
in the vicinity of Rye Cove; Mannville School. 
Wardell formation (Hesperorthis zone) in Tennessee: On U. S. Highway 
25E, Evans Ferry section, 0.8 mile north of Indian Creek, Howard Quarter 
(T.V.A. 162-NW) Quadrangle. 
Discussion—Sowerbyella socialis occurs in great numbers in several locali- 
ties. It is characterized by strongly beaded costellae, acute cardinal extremities, 
fairly strong costellae not differeniated into well-marked zones. The species is 
most like S. compacta, and the interiors of the two species are nearly identical. 
It differs from S. compacta in attaining a somewhat larger size and in having 
stronger costellae and stronger beading on their surface. This species is also 
suggestive of S. variabilis but has a thicker shell and more robust form. It is 
also much more strongly costellate. Sowerbyella socialis differs from S. perplexa, 
which it resembles in form and size, in not having its costellae well differentiated 
into zones and in having strong beading not possessed by the Chatham Hill 
species. Sowerbyella socialis should not be confused with S. lebanonensis be- 
cause that is a shorter form and also has its costellae differentiated into zones. 
SOWERBYELLA SOCIALIS CRASSA Cooper, new subspecies 
Plate 200, B, figures 7-14 
Shell of about medium size for the genus, wider than long, and with the length 
equal to about three-fifths the width at the hinge. Cardinal extremities acute, 
often drawn into small ears. Lateral margins indented just anterior to the cardi- 
nal extremity, otherwise straight and oblique; anterior margin broadly rounded, 
occasionally subnasute. Surface marked by costellae of unequal size, from 70 
to 90 on a valve. First and second generations of costellae narrowly rounded 
and high. In 1 mm. at the front of an adult of average size 3 large costellae may 
be counted. Between the larger costellae 1 or 2 smaller ones of a third genera- 
tion may or may not be intercalated. Costellae strongly spinose. 
Pedicle valve moderately convex in lateral profile and forming low swelling 
highest in the middle in anterior profile. Beak inconspicuous; umbo slightly 
swollen. Fold poorly developed, narrow, often not reaching the front margin. 
Valve most convex in the middle and with gentle slopes to the anterolateral and 
front margins. Slopes to the cardinal extremities long and gentle. Cardinal 
extremities flattened. Interarea long, slightly curved, moderately apsacline. 
Brachial valve with moderate concavity, greatest in the midregion; distinctly 
sulcate in some specimens. Sulcus narrow, may or may not reach the anterior 
margin. Areas bounding most deeply concave part gently concave. Cardinal 
extremities flattened, deflected toward the pedicle valve. 
Interior like that of S. socialis. 
