PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 355 
anterior profile. Median sulcus deepest in the posterior half, becoming shallower 
and wider anteriorly and occupying about one-fourth the width at the front. 
Flanks bounding sulcus strongly folded for the genus. Posterolateral slopes 
concave, gentle. 
Measurements in mm.—Holotype, length 14.1, brachial length 12.0, width 15.7, 
hinge width 14.0, thickness 6.8. 
Types.—Holotype: 109986. 
Horizon and locality——Lincolnshire formation in Tennessee: Evans Ferry, 
U. S. Highway 25F, about 1 mile north of Indian Creek, Howard Quarter 
(T.V.A. 162-NW) Quadrangle. 
Discussion.—This species is distinguished by the numerous closely crowded 
costae, the deep sulcus, and the strongly carinate pedicle valve. It is somewhat 
similar to H. biconvexa but is more carinate, has a deeper sulcus and more 
closely crowded costae. 
HESPERORTHIS QUADRATA Cooper, new species 
Plate 50, K, figures 47-54 
Shell of about medium size for the genus, length and width about equal ; hinge 
forming the greatest width; cardinal extremities slightly auriculate; sides nearly 
straight ; anterior commissure sulcate; anterior margin narrowly rounded; sur- 
face marked by 28 to 32 rounded costae separated by spaces narrower than the 
costae. 
Pedicle valve unevenly convex in lateral profile, the posterior half having the 
greater convexity ; anterior profile narrowly convex and with steep lateral slopes. 
Umbonal region swollen, the swelling continued anteriorly along the median 
portion as a low fold; cardinal extremities not flattened but forming a part of the 
steep and long umbonal slope. Interarea long, slightly curved, strongly apsacline. 
Pseudodeltidium moderately long. Interior with short, receding dental plates. 
Brachial valve gently concave in lateral and anterior profiles; umbo sulcate, 
the sulcus deepening and widening anteriorly to the front margin where it is 
moderately deep and somewhat V-shaped; 5 or 6 costae occupy the sulcus ; flanks 
bounding sulcus flattened; posterolateral extremities very slightly deflected in 
the direction of the pedicle valve. Interior with the usual features of the genus. 
Measurements in mm.—Holotype, length 12.9, brachial length 10.0, width 12.7, 
hinge width 13.3, thickness 6.4. 
Type—Holotype: 116921. 
Horizon and locality.—Lebanon formation in Tennessee: Cut on U. S. High- 
way 241, 2.1 miles north of the Bedford-Rutherford County line in Rutherford 
County ; Lebanon; cut and quarry on U. S. Highway 41, 12 miles southeast of 
Murfreesboro ; south side of U. S. Highway 70S, 4 to $ mile east of Readyville ; 
Columbia; south of Aspen Hill; Lavergne; near Prospect; Tennessee High- 
way 16, 5.1 miles north-northwest of Shelbyville; 13 miles west of Spring City, 
Sequatchie Valley ; Shelbyville; U. S. Highway 70S, 4 mile east of Rutherford- 
