780 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Creek, center subquad., Powder Springs (T.V.A. 154-SW) Quadrangle; Syca- 
more Creek, northwest corner Maynardville (T.V.A. 145-SE) Quadrangle; 
north side of Lone Mountain Creek, just west of the road to Straight Creek, 
0.8 mile west of Lone Mountain Station, Tazewell (T.V.A. 154-NE) Quad- 
rangle. 
Type Ottosee shale (= Benbolt formation) in Tennessee: At Chilhowee Park, 
north side of Knoxville, Knoxville (T.V.A. 147-NW) and Fountain City 
(T.V.A. 146-SW) Quadrangles. 
Discussion.—This is a somewhat variable species, some of the specimens hav- 
ing a fairly quadrate form whereas others are distinctly subrectangular. The 
species is characterized by moderate convexity and concavity, the common sower- 
byelloid habit, but marked by very fine costellae, 6 or 7 to the millimeter. The 
species is much like S. socialis in form and contours but differs in having much 
finer costellae. Sowerbyella lebanonensis is suggestive of this species but has 
costellae more distinctly differentiated into fine and strong and is a more trans- 
verse shell having a length/width index of 0.62 to 0.67, whereas that of S. com- 
pacta is 0.64 to 0.80 and with an average near 0.70. 
SOWERBYELLA CURDSVILLENSIS (Foerste) 
Plate 201, A, figures 1-13 
Plectambonites curdsvillensis Forrste, Bull. Sci. Lab., Denison Univ., vol. 17, p. 122, pl. 10, 
figs. 15A, B, 1912. 
In describing this species Foerste failed to give any details of the exterior. 
His description emphasizes the subperipheral border and the small pallial dis- 
tributaries extending anteriorly on its surface. This species is a large form with 
beaded costellae like S. punctostriata. The following characters of the exterior 
are important: Wider than long, with the cardinal extremities nearly a right 
angle; auriculate in the young; subrectangular; sides nearly straight to moder- 
ately oblique ; anterior margin broadly rounded to nearly straight. Pedicle valve 
fairly strongly convex in lateral profile; broadly convex in anterior profile; lat- 
eral slopes long and moderately steep. Brachial valve moderately deeply con- 
cave ; flanks gently concave to somewhat flattened. 
Inside the pedicle valve the diductor scars are long and separated by a median 
ridge extending nearly to the valve middle; vascula media broad. Brachial in- 
terior usually with thickened subperipheral rim, well-defined septa and wide ad- 
ductor field with elevated rim marking its outer boundaries. 
Types.—Figured hypotypes : 117491b,c,e,g-i; unfigured hypotypes: 117491A4,4d,f. 
Horizon and locality.—Curdsville formation in Kentucky. 
Basal Martinsburg formation (=Curdsville): Along the Cumberland front 
and elsewhere in Virginia and Tennessee. 
Discussion.—The differences between this species and S. punctostriata are 
discussed on page 792. The two species are sufficiently close to be ecads of a 
single species, but larger collections than those available in this study will be 
necessary to demonstrate the point. 
