832 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
exterior will have to await the discovery of more favorably preserved specimens. 
Information on the interior is also lacking except for the cardinal process. The 
holotype is large for the genus, with the hinge forming the widest part and the 
lateral margins sloping gently toward the middle. The anterior margin is broadly 
rounded. The surface shows distant costellae and faint traces of finer ones be- 
tween the larger ones. 
The pedicle valve is strongly convex with the greatest convexity located 
slightly anterior to the middle; inasmuch as the body of the shell is not clearly 
marked from the geniculated portion by an abrupt change of curvature, it is 
difficult to place the position of geniculation, but it appears to be about 8 to 
IO mm. anterior to the beak. The body of the shell is gently convex in profile 
and has a slightly swollen umbonal region. The anterior sloping part or trail is 
moderately steep, with the steepest parts toward the anterolateral extremities. 
Angle of geniculation 120°. Interarea short, apsacline. 
The brachial valve is strongly geniculated at an angle of about 130° about 
10 mm. anterior to the beak; the deflected part is steep and makes a rim about 
6 mm. wide around the body of the shell which is flat to slightly concave. 
Measurements in mm.—Holotype, length 18.3, brachial length 13.2, width 23.8, 
hinge width 22.7, thickness 5.0, surface length 22.5. 
Type—Holotype: 71505. 
Horizon and locality—Little Oak formation in Alabama: 4 mile north of Pel- 
ham, Bessemer Iron District (15’) Quadrangle; junction Bailey Gap and Cahaba 
Valley roads, 1% miles northeast of Newhope Church, SW4SW34 sec. 13, 
T. 19 S., R. 2 W., Vandiver (15’) Quadrangle. 
Discussion.—This species is characterized by large size, wide hinge, strong 
convexity of the pedicle valve, and gentle concavity of the brachial valve. This 
species suggests D. obtusa but differs in angle of geniculation and is larger, less 
deep, and with more oblique sides. 
DACTYLOGONIA OBTUSA Cooper, new species 
Plate 216, C, figures 8-13; plate 217, L, figures 35-37; plate 220, A, figures I-5 
Shell large, variable, wider than long with the hinge forming the widest part; 
lateral margins sloping moderately toward the middle or slightly rounded; an- 
terior margin broadly rounded. Surface costellate, costellae rounded and sepa- 
rated by spaces narrower than the costellae; on the pedicle valve costellae alter- 
nate in size, I or 2 smaller ones alternating with the larger ones, but on the 
brachial valve the costellae are more uniform in appearance and more crowded 
with less differentiation between the larger and smaller ones. 
Pedicle valve geniculating about 11 mm. anterior to the beak; angle of genicu- 
lation obtuse, about 95 to 100°; visceral portion moderately convex, umbo and 
beak slightly swollen ; a low, indistinct median fold extends anteriorly for about 
a quarter the length but in some specimens is distinguishable for the length of 
the body of the shell. Median part of shell body slightly swollen with gentle 
slopes to the margins. Geniculated part or trail convex in profile, and with steep- 
