840 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Hills road to Lexington, 14 miles northwest of Lexington, Lexington (15) 
Quadrangle. 
Discussion——This species suggests D. geniculata, but the brachial valves are 
more concave, the geniculation is less sharp, and the trail shorter. 
DACTYLOGONIA sp. 8 
Plate 216, A, figures 1-4 
Shell small for the genus, wider than long; visceral region of both valves 
marked by more or less obscure concentric wrinkles. Visceral region of pedicle 
valve flat in lateral profile ; point of geniculation about 6 mm. anterior to the beak; 
angle of geniculation about 95° ; trail moderately long, convex in profile. Place of 
geniculation marked by a slight rim. Brachial valve with visceral part nearly 
flat. Umbo and median part gently sulcate ; trail narrowly and sharply deflected. 
Measurements in mm.—117613a, length 7.9, brachial length 7.0, midwidth 
10.9, hinge width 12.0, thickness 2.3, surface length 10.5, trail length 5.0. 
Figured specimen.—117613a. 
Horizon and locality—FPoteet formation (Yellow Branch member) in Vir- 
ginia: Along the Yellow Branch road, 5 miles southeast of Rose Hill (T.V.A. 
161-NE) Quadrangle. 
Discussion—The size and visceral region of this species suggest D. palustris, 
but geniculation is too sharp and the trail too long. 
CYPHOMENA Cooper, new genus 
(Greek kyphos, bent; mene, crescent) 
Shell generally transversely subrectangular in outline, concavo-convex in pro- 
file; valves strongly geniculated toward the brachial valve. Surface marked by 
fine subequal radial costellae crossed by fine concentric lines. Costellae not 
grouped into zones of different sizes as in Dactylogonia. Pseudopunctate. 
Pedicle valve with small but stout teeth; thick plates extend as a rim nearly 
completely around the suboval muscle field. Diductor scars subcrescentic, elon- 
gate, located on each side of a short, low median ridge which divides the muscle 
field but is extended anteriorly for a short distance only. Incipient vascula media 
extend directly anteriorly from the anterior ends of the diductors. Foramen and 
pseudodeltidium leptaenoid. 
Brachial interior with broad, shallow sockets, the inner wall of which is formed 
by the outer face of a broad, flat brachiophore ; notothyrial cavity filled by a thick 
platform which supports the cardinal process and nearly buries the brachiophore 
with lateral extensions. Median ridge short, extending from notothyrial plat- 
form and dividing the posterior adductors. Cardinal process formed of 2 nar- 
row, short-shafted pieces with flat myophores. Chilidium strongly convex and 
covering part of the myophore surfaces. Adductor field narrowly triangular or 
arrow shaped in outline with the apex directed anteriorly; posterior adductors 
the larger, located outside the anterior pair and apparently divided into pairs 
