PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 449 
Types.—Holotype: 11082Ir; figured paratypes: 11082In,0,q,s; unfigured 
paratypes: 110821a-m,p,t,u. 
Horizon and locality—Arline formation in Tennessee: Along wagon road in 
glade, 4 mile southeast of Friendsville, Concord (T.V.A. 138-SW) Quadrangle; 
McMullens, Meadow (T.V.A. 139-NW) Quadrangle. 
Discussion—This species is fairly common at Friendsville and can be recog- 
nized by its compact form, strongly convex valves, and thick costae. The last- 
named feature and the depth of the valves distinguish it from P. australis. 
The species is suggestive of P. ponderosa in its compact form but does not reach 
the large size of that species. It is quite unlike any other species described herein, 
which in general remind one more of P. plicatella than the compact forms. 
PLECTORTHIS LEBANONENSIS Cooper, new species 
Plate 81, D, figures 15-17 
Shell fairly large for the genus, wider than long; hinge narrow; valves un- 
equally convex, the pedicle valve with the greater convexity. Sides gently 
rounded ; anterior margin broadly rounded ; maximum width at about the middle. 
Surface marked by about 30 narrowly rounded costae separated by spaces equal 
to or slightly greater than the width of the costae, those of the brachial valve 
slightly more distantly spaced than those of the pedicle valve. Interspaces marked 
by fine, elevated threads. 
Pedicle valve strongly convex in lateral profile with the greatest convexity in 
the posterior region; anterior profile strongly convex; umbonal and median re- 
gions inflated; lateral areas somewhat inflated and with moderately steep but 
short slopes. Interarea curved, apsacline. 
Brachial valve gently convex in lateral profile; broadly and gently convex in 
anterior profile; sulcus originating at the umbo, shallow and extending to the 
anterior margin ; flanks bounding sulcus gently swollen; lateral slopes moderately 
long but gentle. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Laieiiei9 ¢ sila luge Seelam alpen «Ae jaar ? 10.2 8.4 he 
Paratype ''(T10834a) 5.2.08. ? 8.7 12.0 IT. #2? 
Types.—Holotype: 110834c; figured paratypes: 110834a,b. 
Horizon and locality.—Lebanon formation in Tennessee: On Tennessee High- 
way 16, 3.6 miles northwest of junction of Tennessee Highway 16 and U. S. 
Highway 241, Shelbyville, Bedford County; quarry on U. S. Highway 41, 11.7 
miles southeast of Murfreesboro, Rutherford County. 
Discussion—The specimens on which this species is based leave much to be 
desired, but the species is fairly distinctive in the slender and closely crowded 
costae. Most of the specimens are young, but a few indicate that the species must 
have reached an adult width of nearly 20 mm. The species is characterized, be- 
sides the costae already mentioned, by the strongly convex pedicle valve and 
