PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 635 
or 3 costae occurring in the sulcus. Fine ornamentation consisting of irregular 
concentric fila. 
Pedicle valve very gently convex in lateral profile with the greatest convexity 
between the beak and the middle. Umbonal region and posterior third gently 
convex ; sulcus originating 7 to 8 mm. anterior to the beak, widening and deep- 
ening rapidly to occupy slightly more than half the valve width. Tongue long, 
truncated anteriorly, and in old shells somewhat flattened to form a broad base. 
Flanks narrowly rounded with strongly pointed anterolateral extremities. Slope 
to margins nearly flat and nearly vertical to the commissure, and marked by 4 
or 5 obscure costae. Beak incurved; delthyrium open. 
Brachial valve gently convex in lateral profile and with the greatest convexity 
located at about the middle; anterior profile with a flattened top and nearly verti- 
cal sides. Fold originating at 4 to 5 mm. from the beak, scarcely perceptible near 
the middle of the valve and becoming more elevated anteriorly but never strongly 
set off from the body of the valve. Two median costae of sulcus often slightly 
depressed below the bounding costae. Flanks narrowly rounded with the antero- 
lateral extremities elongated in the direction of the pedicle valve and, with the 
fold, forming a deep reentrant that accommodates the tongue of the pedicle valve. 
Sides steep and nearly vertical to the commissure. Umbo sulcate. 
Interior: Teeth small, dental plates well developed but short and confined to 
the sides of the valve, forming narrow slitlike umbonal cavities. Delthyrial cavity 
occupied by pedicle callist; muscle field located anterior to callist and dental 
plates ; adductor scar small, oval, located in the posteromedian position next to 
the callist. Diductor scars large, flabellate, and surrounding other scars. Acces- 
sory diductors located in front of and on each side of the adductor scar. 
Hinge plate divided, the halves supported by short plates attached to their 
under side and to the median septum to form a narrow chamber ; outer side of 
hinge plates attached to side of valve by well-defined fulcral plates. Socket plates 
stout ; outer hinge plates triangular, gently concave, giving off long slender crura 
from their inner side. 
Measurements in mm.— 
Brachial 
Length length Width Thickness 
Hightech ws ottade oid Wo. awake 12.7 11.4 II.9 8.6 
Paratype (GILTAGS ) s <:d.s.+ ee aan 12.1 10.9 11.0 9.9 
= WERE ADEE ) cs tot 5. -sithisn gece 6.9 5.1 5.9 3.5 
i GINEADEA sac sans ans cise 13.7 i239 13.3 10.0 
Types.—Holotype: 111481a; figured paratypes: 111462a-c, 111468, 111481c; 
unfigured paratypes: 111480a,b, 111481b,d. 
Horizon and locality —Lebanon formation in Rutherford County, Tenn.: On 
U. S. Highway 41, ? mile south of Knox Branch, about g miles southeast of 
Murfreesboro; 3 miles east and 3 miles northeast of Murfreesboro; cut and 
quarry on U. S. Highway 41, 12 miles southeast of Murfreesboro; Mount 
Olivet, 10 miles southeast of Murfreesboro on U. S. Highway 41; U. S. High- 
way 241, 14 miles (airline) southwest of Christiana. In Bedford County, Tenn.: 
