PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 601 
Pedicle valve gently convex in lateral profile; broadly and gently convex in 
anterior profile. Umbonal region gently convex; sulcus originating 2 mm. an- 
terior to the beak, deepening rapidly and occupying about half the width at the 
front. Tongue long, bent at an angle slightly greater than a right angle. Sides 
of sulcus opposite place of geniculation of tongue precipitous and bounded by 
an extravagantly developed costa on each side. Flanks gently convex but with 
steep slopes. 
Brachial valve somewhat deeper than the pedicle valve, slightly more convex 
in lateral profile; anterior profile narrowly convex and with steep lateral slopes. 
Umbonal and median region flattened. Fold originating at or near the middle, 
strongly elevated anteriorly and with precipitous sides. Flanks strongly rounded 
and with steep slopes. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Ripiotype). iv. 2 vee eects... bas eei< 5.7 5.5 6.6 1.9 4.4 
Pacatype \CEIZTSOD) oie .n 5 wie.s sinys os 6.2 5.7 6.7 27 5.8 
as ee eats 7) Ee er 6.2 5.7 6.5 2.1 5.3 
‘a (ar7rGed ys 222808) NS 6.0 5.4 7.1 2.2 4.8 
Types.—Holotype: 117186a ; figured paratype: 117186e; unfigured paratypes: 
117186b-d. 
Horizon and locality——Chatham Hill formation in Virginia: 1.2 miles S, 31° 
KE. of Sharon Springs, Burkes Garden (15’) Quadrangle. 
Discussion—This species is characterized by its rotund form and considera- 
ble thickness. It is suggestive of the Benbolt P. aseptata but differs in its greater 
thickness, flattened umbo of the brachial valve, and more extravagantly developed 
fold and sulcus. These features will also differentiate it from P. costata. 
PLECTOCAMARA SULCATA Cooper, new species 
Plate 123, A, figures 1-6 
Shell small, wider than long, sides narrowly rounded; strongly uniplicate; 
costate, with 2 costae in the sulcus, 3 on the fold, and 4 on the flanks. 
Pedicle valve nearly flat in lateral profile with the surface sloping anteriorly ; 
anterior profile gently convex; sulcus originating about I mm. anterior to the 
beak, deepening abruptly, but narrow throughout. Sides of sulcus precipitous; 
costae bounding sulcus produced anteriorly and greatly elevated in a direction 
toward the pedicle valve; flanks flattened but with steep slopes. 
Brachial valve gently convex in lateral profile; moderately convex in anterior 
profile. Fold originating slightly anterior to the middle, abruptly but not strongly 
elevated. Fold narrow and with closely crowded costae. Flanks moderately swol- 
len, depressed anteriorly to emphasize the lateral margins of the fold. 
Measurements in mm.—Holotype, length 4.2, brachial length 3.8, width 5.1, 
hinge width ?, thickness 3.3. 
Type.—Holotype: 117187. 
Horizon and locality.—Benbolt formation in Virginia: On the south side of 
