50 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
rounded; front margin truncated, posterolateral margins forming an 
obtuse angle ; paucicostate, having 5 costae on the fold of the brachial 
valve and 4 costae in the sulcus of the pedicle valve, and the flanks 
with 4 costae. 
Pedicle valve gently convex in lateral profile, nearly flat in anterior 
profile ; beak small, incurved ; umbo gently swollen ; sulcus originating 
just anterior to the middle and occupied by 4 costae; costae extending 
posteriorly for a short distance onto the umbo. Tongue long, genic- 
ulated at right angles, truncated anteriorly; flanks bounding sulcus 
not strongly elevated, flattened. 
Brachial valve moderately convex in lateral profile but strongly 
convex in anterior profile ; umbo smooth and swollen; fold originating 
at about the valve middle, nearly flat in anterior profile and only 
moderately elevated; flanks gently rounded but sloping steeply to 
the margins. 
Measurements in mm.—Holotype, length 10.5, brachial valve length 
9.5, maximum width 12.0, thickness 7.8; paratype, U.S.N.M. 125467b, 
length 9.8, brachial valve length 8.9, maximum width 10.7, thick- 
ness 9.1. 
Types Holotype, U.S.N.M. 125467a; unfigured but measured 
paratype, U.S.N.M. 125467b. 
Locality. — S87. 
Discussion.—This species is characterized by its globular form, its 
low fold, and the presence of 4 costae in the sulcus and 5 on the fold. 
This species has an exterior resemblance to W. pinguis (Girty) and 
W. shumardiana (Girty) but it differs from both of them in being 
much smaller and in having more costae in the sulcus and on the fold. 
Allorhynchus? permianus Stehli has a fold and sulcus with a similar 
number of costae but this species is costate over the umbones as well 
as on the anterior half. Furthermore, Stehli’s species has more 
costae on the flanks than the Oregon species. No other described 
W ellerella is close to this one. 
Superfamily STENOScISMATACEA Shrock and Twenhofel, 1953 
Family STENOSCISMATIDAE Muir Wood, 1955 
STENOSCISMA MUTABILE OREGONENSE Cooper, new subspecies 
Plate 9C, figures 15-28 
Shell of about medium size for the genus, body slightly wider than 
long, somewhat triangular in outline with beak and sides forming an 
angle of about go°; greatest width anterior to the middle; postero- 
lateral margins narrowly rounded; front margin nearly straight. 
