PART = CHAZYAN AND RELATED BRACHIOPODS—COOPER 783 
forming an acute angle, produced slightly into small points or ears. Surface 
marked by costellae of unequal size, the larger ones separated by I to 5 of the 
finer ones. In addition to the radial markings the surface is covered by very 
fine concentric fila and up to 7 short, oblique wrinkles along the posterior mar- 
gins on each side of the hinge. 
Pedicle valve with moderate curvature in lateral profile and forming a broad, 
gentle arch in anterior profile. The beak is inconspicuous and only very slightly 
produced beyond the posterior margin. Umbo low and broad, not easily dis- 
tinguished from body of shell. Midregion and flanks somewhat swollen; slopes 
to cardinal extremities steep. Anterior slope steep. Interarea not much longer 
than that of the brachial valve, short, apsacline. Pseudodeltidium nearly obsolete. 
Brachial valve moderately concave with the concavity greatest at about the 
middle ; flanks gently concave and anterolateral areas somewhat flattened. Cardi- 
nal extremities very slightly deflected. Interarea hypercline, nearly as long as 
the interarea of the pedicle valve. 
Interior: Pedicle valve with delthyrial cavity wide, partially filled by callus 
deposit ; median ridge very thin in the young, well thickened in the adult, ex- 
tending about one-third the length of the valve. Ridges bounding outside mar- 
gin of diductor-adjustor field short and stout; diductor-adjustor field wide and 
long extending to the middle of the valve. Shell thickened and papillose just 
inside the anterolateral margins. 
Brachial valve interior with median ridge and lateral septa low; shell not 
greatly thickened in the young but strongly thickened in old shells forming a 
strong subperipheral border on the sides and toward the front and a steep an- 
terior slope. In old shells medium septum becoming obsolete and lateral septa 
greatly thickened. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness Height 
MECtOtypen.\s laches stee < eers 73 ? II.5 12.4 ? 1.5? 
Hypotype (117497a)... 6.8 ? 10.1 11.2 fe ? 
CEI74075) wsteu..2 7.0 12.1 13.2 ? Ts 
‘ (1274070) ac ak 7.9 LAg 122 ? ? 
: (117494a)... 9.1 8.2 14.4 15.3 2.2 3.2 
Types—Lectotype: 80487a, paratypes: 80487b-d; figured hypotypes: 
117494a-c, 117495a, 117496a, 117497c; measured hypotypes: 1174972,b. 
Horizon and locality.—Lebanon formation in Tennessee: At Shelbyville, Bed- 
ford County; Columbia, Maury County; near Prospect, Giles County; near 
Bradyville, Cannon County; LaVergne, Rutherford County. Cut on U. S. 
Highway 241, 2.1 miles north of Bedford County line; U. S. Highway 70S, 
14 miles east of Brinkley School, east of Murfreesboro; near Readyville; U. S. 
Highway 70S, 1.65 miles west of Cripple Creek, 1.5 miles west of Kittrell; 
Rutherford County. On Tennessee Highway 16, 1 mile south of Rutherford 
County line. 
Discussion.—This species occurs in great abundance in the lower part of the 
