PART, CHAZYAN AND RELATED BRACHIOPODS—-COOPER 8o1 
regular zones of fine costellae, thus being intermediate between S. negritus and 
S. silicica. 
SOWERBYELLA VULGATA Cooper, new species 
Plate 198, A, figures 1-22; plate 202, C, figures 16-23; plate 206, B, figures 8-12 
Shell of about medium size for the genus, wider than long, hinge forming wid- 
est part; semielliptical in outline; sides gently to moderately oblique; anterior 
margin rounded ; costellae subequal in size, fairly crowded, variable but ranging 
between 5 and 6 to the millimeter at the front margin. 
Pedicle valve fairly evenly and moderately convex in lateral profile; anterior 
profile broadly and gently convex, the median region broadly swollen with gently 
convex, moderately steep alopes. Umbo narrowly swollen, the swelling extended 
anteriorly to form a low fold; interarea steeply apsacline. 
Brachial valve deeply concave and with a fairly well defined sulcus running 
from umbo to anterior margin; flanks moderately concave. 
Pedicle interior with wide and short diductor scars and moderately long, thick 
septum separating them. Brachial interior with low median septa and broad and 
long adductor scars. Anterior slope long and fairly steep. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
TLOLOEY Pe, «isis lcie ste toe 7.4 7.0 II.0 12.5 1.5 2.2 
Paratype (117543b).. 7.2 6.9 10.5 11.4? 1.6 ae 
(TI75431) <: 6.3 6.0 9.1 9.7 1.6 1.9 
ie (117543g).. 6.4 6.1 10.0 ELT es 2.0 
ok CET7SA08 ice) IEE 6.9 II.0 13.0 1.5 2.4 
ie (at7s4ta).. 63 6.1 10.4 12.0 1.4 2.0 
i (11754Ie).. 6.9 6.4 10.0 12.2 1.5 2.2 
Types.—Holotype: 1175438, figured paratypes: 117540a-d, 117541a, 1175422, 
b,e, 117543b-d,f; unfigured paratypes: 117541b-e, 117542c,d, 117543¢,g. 
Horizon and locality Bromide formation (Mountain Lake member) in Okla- 
homa: In the road cut on Oklahoma Highway 18, 1.8 miles south of Sulphur, 
Murray County; Spring Creek, N3 sec. 17, T. 2 S., R. 1 W., Murray County ; 
Mountain Lake, E} sec. 22, T. 2 S., R. 1 W., Carter County; on Tulip Creek, 
SWIiNWIiNE4 sec. 25, T. 2 S., R. 1 E., Carter County. 
Discussion—This is a variable species characterized by moderate size and 
convexity, moderately concave brachial valve and poorly differentiated costellae. 
It differs from S. plicatifera and S. variabilis, both Oklahoma species, in lack- 
ing marked differentiation of the costellae. The species is suggestive of S. com- 
pacta of the Appalachian Valley region in size, shape, and profiles but is a more 
deeply concave and less robust species. It differs from S. socialis in having 
much finer and less strongly beaded costellae. 
The costellae of this species are somewhat variable, specimens occurring with 
moderately strong costellae but others in which the radii are distinctly finer. No 
clear-cut separation between the two kinds proved possible and they are regarded 
as constituting one species. 
