PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 797 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness Height 
Holotype. seit ve. eek 8.0 78 11.3 14.0 1.8 2.4 
Paratype (117528b).. 7.1 6.8 10.5 12.4 1.8 2.1 
Types.—Holotype : 117528a; figured paratype: 117529b; unfigured paratypes: 
117528b; 1175292. 
Horizon and locality —Wardell formation and Wardell part of Dryden forma- 
tion in Virginia: At Rye Cove and vicinity. Same formation in Tennessee: 
50 yards north of the intersection at Thorn Hill on U. S. Highway 25E, Avon- 
dale (T.V.A. 162-SW) Quadrangle. 
Discussion.—This differs from S. socialis in its still stronger costellae and 
the prominent beading on the fine costellae. 
SOWERBYELLA SUBCARINATA (Ulrich) 
Plate 200, C, figures 15-18 
Plectambonites subcarinatus Ulrich (Ms.) in Butrs, Alabama Geol. Surv., Special Rep. 14, 
p. 126, pl. 31, figs. 9-15, 1926. 
Although this species has been figured, it has never been described. The type 
lot contains 6 specimens, not one of which is well preserved. The adult speci- 
mens are all badly exfoliated, and the interiors are of young specimens. Con- 
sequently, the species is difficult to define. Despite these difficulties the feature 
that gives the specific name to the species—the narrow median fold—is suff- 
ciently well developed to be distinct even in the peeled specimens. A descrip- 
tion of the type material and a few additional topotypes is given below. 
Shell of about medium size for the genus, wider than long but with the length 
and width variable. Cardinal extremities acute and often produced into small 
ears. Lateral margins nearly straight to oblique. Anterior margin broadly 
rounded, usually nasute. Surface multicostellate; costellae elevated, narrowly 
rounded, slightly narrower than the interspaces. Costellae in 3 generations; 
costellae of first 2 generations of about the same size at the margin; I to 2 
costellae of the third generation intercalated between those of the first 2 along 
the margin. Costellae 6 to 10 in a millimeter at the front and from 80 to 120 
in number. Spaces between costellae marked by moderately distant, elevated con- 
centric fila. 
Pedicle valve moderately strongly convex in lateral profile and with the great- 
est convexity in the posterior half. Anterior profile strongly convex with a 
hump at the middle, the sides convex and sloping moderately to the lateral mar- 
gins. Median fold narrow, strong, often producing the front margin into a small, 
blunt nose. Umbo narrowly swollen; beak inconspicuous. Regions bounding 
sulcus swollen but not raised above level of fold; slopes to cardinal extremities 
steep. Interarea apsacline. 
Brachial valve with greatest convexity along line of sulcus corresponding to 
the fold; flanks bounding sulcus gently convex or somewhat flattened. Cardinal 
extremities deflected. 
