PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 547 
Pedicle valve evenly and gently convex in lateral profile; anterior broadly and 
gently convex. Umbo narrowly convex, small; sulcus originating 2 to 24 mm. 
anterior to the beak, deepening rapidly to the front margin where it occupies 
less than half the shell width. Sulcus bounded by a prominent elevated plication 
occupied by 2 or more costellae; flanks gently concave. Interarea long, moder- 
ately apsacline. 
Brachial valve gently convex in lateral profile with the umbo swollen but not 
strongly protruberant ; anterior profile broadly and gently convex. Umbo swollen 
and small; fold originating on the anterior side of the umbo, elevating rapidly 
toward the front margin where it is high and with precipitous sides. Sulci at 
base of folds moderately deep and prominent, producing narrow lobes. Flanks 
gently swollen; posterolateral extremities somewhat flattened to perceptibly 
concave. 
Measurements in mm.—Holotype, length 15.5, brachial length 13.9, width 21.2, 
hinge width 15.9, thickness 9.6. 
Type.—Holotype: 117109. 
Horizon and locality —Shippensburg formation (Pinesburg member—Echino- 
sphaerites zone) in Maryland: Road cut on U. S. Highway 40 at Wilson on the 
west side of Conococheague Creek, 7 miles west of Hagerstown, Williamsport 
(15’) Quadrangle. 
Discussion.—This species may be recognized by the strength of the costellae, 
the fairly narrow and elevated fold, and deep sulcus. The species is broadly 
shouldered but its profile somewhat compressed. It differs from O. simulatrix 
(Bassler), which has a high fold, in the greater strength of the costellae and in 
the less rotund profile. Oxoplecia pennsylvanica is strongly costellate and ap- 
proximately the same size as O. magnaplicata, but it has more convex valves, 
lesser width, and a deeper sulcus. 
OXOPLECIA MARMORATA Cooper, new species 
Plate 103, B, figures 13-16 
Shell of small to medium size for the genus, wider than long and with a broadly 
elliptical outline ; sides narrowly rounded ; anterior margin broadly rounded ; sur- 
face strongly and completely costellate; numerous costellae bifurcating near the 
front margin; flanks with as many as 15 costellae; sulcus with 3 to 6 and fold 
with 4 to 7 costellae. 
Pedicle valve moderately convex in lateral profile and broadly and gently con- 
vex in anterior profile ; umbo narrow; sulcus originating 2 to 3 mm. anterior to 
the beak, wide and shallow, and occupying at least half the width. Flanks flat 
and with gentle slopes. 
Brachial valve moderately convex in lateral profile but fairly strongly convex 
in anterior view; umbo swollen; fold broad and gently rounded, not strongly 
separated from the flanks, only gently elevated. Flanks inflated and with steep 
lateral slopes. 
