774 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Family SOWERBYELLIDAE Opik, 1930 
Plectambonitacea having a simple cardinal process united to the brachial proc- 
esses, giving the cardinalia the shape of an inverted V. 
Subfamily SowERBYELLINAE Opik, 1930 
Sowerbyellidae having 2 or more septa in the brachial valve. 
Genus SOWERBYELLA Jones, 1928 
Sowerbyella Jones, Mem. Geol. Surv. Great Britain, Paleont., vol. 1, No. 5, pp. 384, 302, 
1928. 
SOWERBYELLA AEQUICOSTELLATA Cooper, new species 
Plate 199, B, figures 9-17 
Moderately large, length equal to about two-thirds the width. Cardinal ex- 
tremities somewhat rounded, slightly acute or approximating a right angle. Lat- 
eral margin gently convex ; anterior margin broadly rounded. Anterior commis- 
sure rectimarginate. Surface multicostellate; costellae narrowly rounded, sepa 
rated by narrower interspaces. Costellae of nearly equal size. A few stronger 
than the surrounding ones are scattered on the surface. Costellae numbering 
about 24 to 30 in 5 mm. at the front margin. 
Pedicle valve strongly convex in lateral profile and with the greatest con- 
vexity posterior to the middle. Anterior profile with the greatest convexity at 
the middle and with the lateral slopes flat and moderately steep. Beak incon- 
spicuous, protruding very slightly beyond the posterior margin. Umbonal and 
median region inflated. Lateral areas moderately inflated with the slopes to the 
cardinal extremities short and moderately steep. Interarea long, curved, gently 
anacline. 
Brachial valve moderately concave with the greatest concavity at about the 
center but becoming concave anteriorly. Flanks gently concave. Interarea mod- 
erately long, hypercline. 
Interior: Pedicle valve with median ridge separating diductors short and 
stout, expanding anteriorly; diductor impressions large, widely divergent; ad- 
ductor impressions small. Cardinal process of brachial valve large, septa low, 
strongly elevated at about the middle of the valve ; adductor impressions thickened 
to form a low platform. Anterior half strongly spinose. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness Height 
EVOLOEY PE...» <Pdisisialevepeyererss 9.2 ee Tgi2 13.2 2.0 3.0 
Paratype (117477a)... 7.3 ? 11.7 12.2 ? ? 
a (117477b)... 8.6 ? 137 13.5 fe G 
AA (117477c)... 8.0 ? 13.2 13.6 ? ? 
es (174770)... 7 8.7 14.3 14.5 ? ? 
¥ (117477g)... 8.5 viel 13.4 12.6 2.6 3.5 
Types.—Holotype: 117477{; figured paratypes: 117476a, 117477a,b,d,e,g ; un- 
figured paratypes: 117476b-d, 117477¢,h. 
