PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 535 
Pedicle valve oval in outline with uneven lateral profile, the greatest depth in 
the median region; anterior profile moderately convex; median region inflated ; 
sulcus broad and shallow; tongue short and rounded. 
Brachial valve broadly elliptical, width slightly greater than length; lateral 
and anterior profile strongly convex ; valve deep and tumid ; umbonal and median 
regions inflated and with precipitous slopes to the margins. Fold inconspicuous 
and short, defined at the anterior quarter only ; plication of anterior commissure 
deep. 
Measurements in mm.— 
Brachial 
Length length Width Thickness 
Holotype (brachial valve) ......... ? E 8.4 4.4 
Paratype (pedicle valve) .......... 5.6 ? 5.3 7 
Types.—Holotype: 117090b ; figured paratype: 117090a. 
Horizon and locality—Row Park formation (Maclurites bed) in Pennsyl- 
vania: About 175 feet above the “Mosheim” limestone at the base of the Row 
Park formation, 4 to 4 mile east-northeast of the railroad cut, 24 miles southwest 
of Marion, Chambersburg (15’) Quadrangle. 
Same formation in Maryland: From the Maclurites bed in the ledge over- 
looking the Potomac River in quarry at Pinesburg Station, Williamsport (15’) 
Quadrangle. 
Discussion.—This species is larger and unlike other described species of Ony- 
choplecia. It is characterized by its fairly flattish pedicle valve, and extremely 
swollen but well-rounded brachial valve. In the latter respect it differs from 
Triplesia carinata from Pratt Ferry, Ala., which it resembles. The southern 
species is characterized by its extreme depth, but it has a strong subcarinate fold. 
The Pennsylvania species, on the other hand, has a tumid brachial valve but the 
fold is inconspicuous on the body of the shell and may be seen only at the front 
margin where it shows as a wave of the commissure. Differences of these sorts 
in the brachial valves indicate that the pedicle valves, too, will be quite unlike. 
The sulcus of O. obesa is short, wide, and shallow; that of Triplesia carinata, on 
the other hand, is deep, wide, and has a strong median groove within the sulcus. 
ONYCHOPLECIA TENUIS Cooper, new species 
Plate 100, K, figure 50 
About medium size for the genus, tear-shaped in outline with rounded sides 
and attenuate beak forming an angle of slightly more than 70°. Anterior com- 
missure perceptibly uniplicate with a suggestion of costation along the margin. 
Surface smooth. 
Pedicle valve gently convex in lateral profile with the maximum convexity in 
the median region; anterior profile more convex than that of the lateral view, 
broad and moderate. Umbonal region somewhat flattened; median region some- 
what swollen; lateral slopes gentle. Sulcus in an incipient stage. Beak long; 
pseudodeltidium with narrow longitudinal elevation. 
