PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 455 
to the middle of the valve. Anterior profile with flanks sloping gently away from 
the swollen median region. Fold barely perceptible. Beak slightly incurved ; 
interarea moderately long, apsacline, slightly curved. 
Brachial valve with lateral profile having its greatest convexity at about the 
middle. Sulcus originating on the umbo near the beak and extending to the front 
margin where it is visible as a slight depression occupied by 5 costae. Flanks 
bounding sulcus slightly swollen and lateral slopes of flanks to the posterolateral 
margin short and consequently moderately steep. 
Measurements in mm.—Holotype, length 13.2, brachial length 12.1, width 
18.1, hinge width 12.4, thickness 6.3. 
Types.—Holotype: 98181. 
Horizon and locality—Arline formation in Virginia: Quarry at Marion, 
Marion (T.V.A. 218-SE) Quadrangle; Ward Cove formation 0.4 mile northeast 
of Jeff Gillespie’s in Thompson Valley, southwest of Tazewell, Pounding Mill 
(15’) Quadrangle. 
Discussion.—This species is characterized by its transversely elliptical out- 
line. It approaches P. compacta in size but is more slender and less coarsely 
costate. This species is also suggestive of P. plicatella of the Trenton but differs 
in its slender profile and more slender costae. 
PLECTORTHIS sp. 1 
Three specimens from the Nidulites zone of the Chambersburg limestone indi- 
cate a species suggesting P. lebanonensis in the form and ribbing of the pedicle 
valve, but the brachial valve is shallow and contains numerous incipient intercala- 
tions at the front margin. 
Measurements in mm.— 
Length Width 
Pedicle -walve Ta7o2ba we. cdl es dar els Sy Ee 11.7 14.7 
ESPACHIAN VALVE: TT7OZOD. 2595.0 sie 2s" > Sagapedaneasiahicauaiea sie =e ee 10.5 14.3 
Described specimens.—117026a,b. 
Horizon and locality Shippensburg formation (Pinesburg member-Nidulites 
zone) in Pennsylvania: 34 miles north of Greencastle, Chambersburg (15’) 
Quadrangle. 
PLECTORTHIS sp. 2 
Plate 84, C, figure 18 
A Plectorthis of uncertain nature occurs in the chert of the Murfreesboro 
formation at the type locality. The specimens consist of three partially buried 
exteriors and the posterior end of a brachial interior which shows the character- 
istic cardinalia. The specimens are so strongly silicified that accurate description 
is not possible. 
Figured specimen.—110835a. 
Horizon and locality—Murfreesboro formation in Tennessee: From exca- 
vation of new armory building at junction of west fork of Stone River and U. S. 
