500 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
fers from S. anthonensis in its more angular outline and stronger folding. It 
differs from S. costatus in the rib development, in having a less convex lateral 
profile than the Virginia form, and in having a stronger fold. The Oklahoma 
species differs from S. convexus in its less rounded lateral profile of the pedicle 
valve and its less deep sulcus. Resemblance to S. rectangulatus is quite strong, 
but the Virginia species has a broader sulcus, squarer outline, and more apsacline 
interarea, 
SKENIDIOIDES PLATYS Cooper, new species 
Plate 98, F, figures 28, 29 
Shell fairly large for the genus, wider than long with the width about 14 times 
the length; cardinal extremities acute; sides rounded and obliquely directed 
toward the middle; anterior margin somewhat nasute; anterior commissure 
deeply sulcate. Costae narrowly rounded and with intercostal spaces about equal 
to the width of the costae; 10 or II costae on the flanks and 8 to 10 on the fold 
and sulcus. 
Pedicle valve barely convex in lateral profile; anterior profile strongly con- 
vex and median region narrowly rounded. Fold wide, prominent, multicostate, 
moderately elevated, formed by a complicated fascicle consisting of an unbifur- 
cated pair on the outside, another unbifurcated pair inside the previous two, and 
a median intercalation all occupying the posterior half. Median intercalated costa 
bifurcating near the middle; the other costae may or may not bifurcate near the 
margin. Flanks flat to gently convex; interarea long and apsacline. 
Brachial valve nearly flat in the posterior half but bent toward the pedicle 
valve when viewed from the side; anterior profile nearly flat; sulcus deep, oc- 
cupying about one-third the width at the front margin; flanks bounding sulcus 
gently convex; posterolateral areas gently convex. Brachial interior with nar- 
row, shallow, and short notothyrial platform. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness 
isletipe ti 25). ve vy rake 3.8 ? 5.4? 5.7 1.9 
Paratype’ (117083a)" occ2)- 27 3.4 3.8 ? 
Types.—Holotype: 117084; figured paratype: 117083a. 
Horizon and locality—Little Oak formation in Alabama on the Bessemer 
Iron District (15’) Quadrangle; 600 feet east of the intersection of the Cahaba 
Valley road with the Helena road, 4 mile north of Pelham; 1 mile north of 
Pelham. 
Discussion.—This species is characterized by its flattened profiles and shallow 
pedicle valve. The species resembles S. halli most but is more strongly costate 
and has a more prominent fold and sulcus as well as less convex profiles. 
SKENIDIOIDES RECTANGULATUS Cooper, new species 
Plate 98, B, figures 6-10 
Shell of about medium size for the genus, wider than long, subrectangular in 
outline with cardinal extremities nearly a right angle, but acute nevertheless ; 
