600 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
PLECTOCAMARA MAGNA Cooper, new species 
Plate 122, G, figures 38-51 
Large for the genus, wider than long, with a transversely but broadly ellipti- 
cal outline; nearly as thick as long. Sides oblique, straight, forming an apical 
angle of 125°. Sides narrowly rounded; anterior margin truncated. Strongly 
uniplicate. Surface costate, 3 costae on the fold, 2 in the sulcus, and 7 on the 
flanks. 
Pedicle valve fairly strongly convex in lateral profile with the maximum con- 
vexity at about the middle. Anterior profile broadly and gently convex; sulcus 
originating about I mm. anterior to the beak, narrow, deepening and widening 
moderately anteriorly where it occupies about one-third the width at the front 
margin. Tongue long and narrow. Sulcus with precipitous sides defined by 
strong marginal subangular costae. Flanks moderately convex and with mod- 
erate slopes depressed below the costae forming the sulcus margin. Spondylium 
moderately large and deep. 
Brachial valve having about the same convexity and depth as the pedicle valve 
in lateral profile ; anterior profile with gently convex top but steeply sloping sides. 
Umbonal region moderately swollen. Fold originating on the umbo, narrow 
and strongly elevated anteriorly, with precipitous sides at the front. Flanks 
moderately swollen and depressed well below the fold. Brachial plates stout ; 
muscle marks deep and prominent. 
Measurements in mm.—Holotype, length 8.0, brachial length 7.3, width 9.5, 
hinge width 2.8, thickness 7.3. 
Types.—Holotype: 117185a; figured paratype: 117185b; unfigured paratype: 
I17185c. 
Horizon and locality.—Base of Shippensburg formation (Pinesburg member- 
Echinosphaerites zone) in Maryland: On U. S. Highway 40, near Wilson on 
the west side of Conococheague Creek, 7 miles west of Hagerstown, Williamsport 
(15’) Quadrangle. 
Edinburg limestone (Cyrtonotella zone) in Virginia: Ravine at the switch 
4 mile east of Strasburg Junction; 0.2 mile east of Strasburg Junction, Stras- 
burg (15’) Quadrangle. 
Discussion.—This species is characterized by its large size and tumid valves. 
Except for P. transversa it is the largest species known. It differs from P. asep- 
tata, which it most resembles, in having a narrower fold and sulcus, more costae 
on the flanks, and a less erect beak. Plectocamara transversa has a wider hinge, 
wider sulcus, and more costae on the flanks than P. magna. 
PLECTOCAMARA ROTUNDA Cooper, new species 
Plate 122, FE, figures 30-34; plate 268, C, figures 7-11 
Large for the genus, slightly wider than long ; transversely and broadly ellipti- 
cal to subcircular in outline. Sides broadly rounded; anterior margin truncated. 
Strongly uniplicate. Surface costate, 3 costae (rarely 4) on the fold, 2 (rarely 3) 
in the sulcus, and 5 to 7 on the flanks. 
