802 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
SOWERBYELLA sp. 1 
Plate 268, A, figures 1, 2 
Small, semielliptical in outline, wider than long; sides gently convex, slightly 
oblique; surface with differentiated costellae, 2 of the larger costellae in the 
space of 1 mm. and the space between the larger costellae occupied by 2 to 4 fine 
costellae. 
Pedicle valve moderately convex and with the greatest convexity at about the 
middle; anterior profile broadly convex, the median region slightly narrowed; 
lateral slopes long and moderately steep. Median region with a narrow but in- 
distinct fold; flanks gently convex. 
Brachial valve moderately concave, deepest in the median region but flattening 
laterally to the posterlateral extremities which are flattened. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
WE PSAAAY oe ete oes 6.8 6.2 9.8 11.4 we 2.2 
LIZ544D BUA Re ai | 6.6 10.2 10.5 1.8 2.4 
Figured specimen.—117544a ; measured specimen: 117544b. 
Horizon and locality—Bromide formation (Mountain Lake member) in Okla- 
homa: 68 to 84 feet above the basal sand on Spring Creek, sec. 17, T. 2 S., 
R. 1 W., Murray County. 
Discussion.—This species suggests S. vulgata but is smaller, more swollen 
medially and umbonally, and with well-differentiated costellae. 
SOWERBYELLA sp. 2 
Plate 204, B, figures 6-12 
Shell of about medium size for the genus, semielliptical in outline; wider 
than long and with the hinge forming the widest part ; cardinal extremities auricu- 
late; sides gently rounded, slightly to moderately oblique depending on age; 
anterior margin broadly rounded; costellae differentiated into fine and coarse, 
2 of the latter occupying I mm. at the front and 2 to 4 of the former visible be- 
tween the larger costellae. 
Pedicle valve gently convex in lateral profile, the greatest convexity located 
just anterior to the umbo and with the front half somewhat flattened. Anterior 
profile forming a low mound highest in the middle and with long, gentle lateral 
slopes. Median region moderately swollen. 
Brachial valve moderately concave and with an indistinct narrow sulcus ex- 
tending from umbo to anterior margin ; flanks moderately concave ; posterolateral 
extremities flattened. 
Measurements in mm.— 
Brachial Hinge \ 
Length length Midwidth width Thickness Height 
MEZGAbAY es oe cee tes 10.7 10.0 14.5 Tog 2.5 3.6 
EIT EASE wake ee 8.4 8.1 11.4 13.4? 1.6 2.3 
