PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 669 
ing and becoming elevated anteriorly to form a prominent but narrow fold in the 
sulcus. Flanks somewhat swollen and with precipitous sides. 
Measurements in mm.—Holotype, length 4.9, brachial length 4.4, width 3.9, 
thickness 2.4. 
Type.—Holotype: 117194. 
Horizon and locality.—Lincolnshire formation (Hogskin member) in Tennes- 
see: On the road to Washburn 2 mile east-northeast of Red Hill, 4 miles west- 
southwest of Thorn Hill, Avondale (T.V.A. 162-SW) Quadrangle. 
Discussion.—The strong costae, fairly large size, and strong inversion of fold 
and sulcus set this species apart from the other members of this genus. 
Family ORTHORHYNCHULIDAE Cooper, new family 
Pedicle valve with small interarea; brachial valve with concave crural bases 
and large cardinal process. 
Genus ORTHORHYNCHULA Hall and Clarke, 1893 
Orthorhynchula Hatt and CuiarKE, Pal. New York, vol. 8, pt. 2, p. 181, 1893. 
ORTHORHYNCHULA LINNEYI (James) 
Plate 128, F, figures 32-36 
Specimens showing the exterior and interior of this genus are introduced for 
comparison with Drepanorhyncha and other rhynchonellids described herein. 
Figured specimens.—87042a, 111352. 
Superfamily Atrypacea Schuchert, 1929 
Family ATRYPIDAE Gill, 1871 
Spiriferacea with widely divergent crura continuous with the primary lamellae 
and with the spiral cones between them. 
Subfamily ZycosPprRINAE Waagen, 1883 
Jugum simple, directed either anteriorly or posteriorly and with the spiralia 
having the apices directed medially. 
Genus ZYGOSPIRA Hall, 1862 
Zygospira HAtt, 15th Rep. New York State Cab. Nat. Hist., p. 154, 1862—Hatt and 
CLARKE, Pal. New York, vol. 8, pt. 2, p. 154, 1893. 
This is a long-ranging genus which appears chiefly in the upper part of the 
tier of rocks under consideration in this monograph. In New York and eastern 
Canada Zygospira is reported earliest in rocks of Lowville age, but it is not 
abundant at this level. In the middle of the overlying Trenton the genus becomes 
abundant. 
In the Southern Appalachians Zygospira appears in abundance in the Witten 
formation and is common or abundant at various levels in the superjacent Ordo- 
