720 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
toward the middle; anterior margin broadly rounded ; surface distantly costellate 
and with fine concentric fila. 
Pedicle valve strongly convex in the median and anterior regions when viewed 
in lateral profile ; anterior profile strongly domed; beak small; fold low and in- 
conspicuous, extending from the beak to the middle; posterior third gently con- 
vex ; median third strongly swollen and anterior third moderately convex; an- 
terior slope steep, much steeper than the longer posterior slope. Interior as usual 
for the genus. 
Brachial valve gently concave in the posterior half, strongly concave in the 
anterior half. Umbo concave; sulcus narrow and shallow, disappearing at or near 
the middle; interarea long, hypercline. 
Measurements in mm.— 
Brachial Surface Mid- Hinge Thick- 
Length length length width width ness Height 
ER OlOty pes ue, ttoen Serer 0723 14.2 ? 24.4 25.3 5.0 7.3 
Paratype (117424a).. 17.8 13.7 24.0? © 23.5 25.4 5-5 7.9 
of (117424d).. 16.7 14.2 22.5 21.0 22.0 4.6 6.8 
Types.—Holotype: 117424e; figured paratypes: 117424b,d; unfigured para- 
types: 117424a,c. 
Horizon and locality—Little Oak formation in Alabama: At the junction of 
the Bailey Gap and Cahaba Valley roads, SWiSW43 sec. 13, T. 19 S., R. 2 W., 
1# miles northeast of Newhope Church, Vandiver (15’) Quadrangle; quarry 
north of Pelham, Bessemer Iron District (15’) Quadrangle. 
Discussion.—This species has about the same size and proportions as T. crassus 
(Willard) but differs in having a more convex posterior half, a more rounded 
geniculated part with a higher but less steep anterior slope. The brachial valve 
of T. convexus is somewhat deeper than that of the Effna species. 
TITANAMBONITES CRASSUS (Willard) 
Plate 181, A, figures 1-9 
Plectambonites crassus WiLLarD, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, 
p. 278, pl. 3, fig. 10, 1928. 
Outline subrectangular, wider than long, hinge forming widest part. Lateral 
margins sloping gently inward, nearly straight. Anterior margin gently and 
broadly rounded. Surface costellate; distantly spaced larger costellae separated 
by numerous finer ones. The larger costellae in the exfoliated condition have 
the appearance of being double. 
Pedicle valve gently convex in posterior three-quarters but strongly genicu- 
lated in the anterior quarter. Point of geniculation about 16 mm. anterior to 
beak ; angle of geniculation about 110°. Beak short, barely protruding posterior 
to the posterior margin. Umbo slightly swollen and melting into the low con- 
vexity of the median area; lateral areas flattened to slightly concave. Anterior 
slope steep, the steepness decreasing posterolaterally as the length of slope de- 
clines. Geniculated slope flat in profile. Interarea long, apsacline. 
