PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 841 
by a more or less thick oblique ridge. Anterior pair elongate and separated by 
a short, low median ridge. 
Genotype.—Leptaena homostriata Butts, Virginia Geol. Surv. Bull. 52, p. 110, 
pl. 95, figs. 24, 25, 1942. 
Discussion—Cyphomena is essentially a side line of Leptaena which never 
developed the concentric wrinkling of the visceral region and which, as far as 
now known, was short lived. Besides the lack of wrinkling, Cyphomena differs 
from Leptaena in lacking the standardized and abrupt geniculation of both valves. 
The brachial valve is more suggestive of Leptaena in its geniculation because it 
has a raised rim on the inside and a precipitous face to the trail. This is not so 
of the pedicle valve, however. 
Inside the brachial valve the musculature is like that of Leptaena including 
the presence of the small longitudinal ridge. The brachial valve shows the 
brachiophores more clearly than most specimens of Leptaena, in which these 
structures are lost or covered. Although the muscle area of the brachial valve 
of the two genera is similar, that of Cyphomena is generally somewhat elevated 
or marked by a thickened rim, emphasizing its arrow-shaped form. 
At the present time Cyphomena is certainly known only from Edinburg and 
Oranda formations in Virginia, Maryland, and southern Pennsylvania. The 
faunas of these two formations are closely related. From the material studied no 
significant evolutional changes were detected during this short interval. A doubt- 
ful species is known from the Chaumont near Montreal, Quebec, Canada. 
CYPHOMENA ANGULATA Cooper, new species 
Plate 224, A, figures 1-8; plate 224, C, figures 21, 22; plate 228, A, figures 1-7 
Shells thick, wider than long and with the hinge forming the widest part; 
cardinal extremities alate; sides gently oblique, anterolateral extremities nar- 
rowly rounded; anterior margin gently convex to gently emarginate. Costellae 
numbering about 4 to the millimeter at the front margin of an adult. 
Pedicle valve strongly convex in lateral profile and with the maximum con- 
vexity near the middle; anterior profile broadly and moderately convex. Umbo 
narrowly convex, the convexity continued anteriorly as a low fold to about the 
place of geniculation 4 or 5 mm. anterior to the beak. Geniculated area broadly 
rounded ; trail moderately long and gently convex ; median region of trail marked 
by a more or less prominent sulcus. Muscle area deeply impressed. 
Brachial valve moderately concave with the most concave part just posterior 
to the place of geniculation. Visceral region gently concave; umbo slightly sul- 
cate; geniculation moderate. Muscle area moderately thickened. 
Measurements in mm.— 
Brachial fst Hinge Thick- Surface Trail 
Length length Midwidth width ness length length 
Folotyper ssh dele. os 10.3 0.2 14.1 15.3 3.0 15.5 9.0 
Paratype (117617a)... 9.7 8.7 12.8 14.8 Z2iG4> LeT3IOL? .. 61078 
Types.—Holotype: 117619a; figured paratypes: 117614a, 117616a, 117617a, 
117618, 117619b; unfigured paratypes: 117614b,c, 117616b,c, 117617b. 
