508 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
terior margin narrowly rounded to nasute. Anterior commissure deeply sulcate; 
lateral commissure gently convex toward the pedicle valve in the posterior half 
but deeply concave toward the pedicle valve in the anterior half. Surface smooth 
or marked by 3 or 4 broad plications on the flanks; the plications may or may 
not reach the anterior margin. 
Pedicle valve deep, gently convex in lateral profile but strongly carinate in 
anterior profile; umbo swollen and beak projecting beyond the posterior mar- 
gin; umbo marked by a more or less prominent ridge or plication that may ex- 
tend onto the fold; fold strongly elevated and prominent, becoming more and 
more elevated anteriorly ; flanks gently swollen in the posterior half and separated 
from the fold by oblique, shallow depressions extending from the side of the 
fold to the anterolateral extremities. Sides of fold steep but only gently convex. 
Interarea long, curved, apsacline ; beak pointed and incurved. 
Brachial valve nearly flat in the posterior half in lateral profile, strongly bent 
toward the pedicle valve in the anterior half; anterior profile broadly and gently 
convex; umbonal and posterolateral areas flattened to faintly swollen; sulcus 
originating near the beak, shallow in the posterior third but widening and deep- 
ening rapidly in the anterior two-thirds ; tongue long and bluntly pointed. Inter- 
area short. 
Interiors as described for the genus. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness 
Holotype th! %, YES toes 1.93 1.60 2.0 2.26 r.3 
Paratype /(117087b). 2eseae: 1.68 1.42 1.93 2.00 1.4 
Types.—Holotype: 117087a; figured paratypes: 117087b-e 
Horizon and locality—Pratt Ferry formation (lower 3 feet) in Alabama: 
0.2 mile south of Pratt Ferry, Blocton (15’) Quadrangle. 
Discussion—No other species of this genus is known. The species is quite 
unlike any known species of Skenidioides in its smooth to plicate ornamentation 
and in the peculiar subpentagonal outline and exceptionally deep sulcus. Speci- 
mens are uncommon in the insoluble residue from the Pratt Ferry limestone. 
PHRAGMORTHIS Cooper, new genus 
(Greek phragma, fence) 
Shell small, biconvex; valves of subequal depth; having the external appear- 
ance of a Dalmanella in the broad sense of the term. Anterior commissure sul- 
cate. Surface multicostellate, some of the costellae swollen. Impunctate. 
Pedicle valve with an elongate interarea and narrow, open delthyrium. Den- 
tal plates short, stout, receding. Muscle area with poorly defined scars ; rounded 
in front, often thickened and elevated a little at the front and joined to the dental 
plates in such a way that the ensemble appears to be a sessile spondylium. Floor 
of the valve thickened for some distance anterior to the muscle field. Vascula 
media oblique, nearly straight. 
