PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 661 
single small costa extending not quite to the middle. Flanks marked by 2 costae, 
I strong one depressed below the 2 bounding the sulcus, and a fine costa on the 
lateral slopes. 
Brachial valve more convex than the pedicle valve, marked by a deep and wide 
median sulcus extending from a point about 4 mm. from the beak to the anterior 
margin; sulcus occupied by a single angular costa that bifurcates at about the 
middle of the valve. Flanks marked by 2 costae fairly strong and a third 
weaker one on the outer slope. 
Measurements in mm.—Holotype, length 4.6+, brachial length 4.6, width 3.0, 
midwidth 2.6, thickness 2.4. 
Type.—Holotype: 118016. 
Horizon and locality.—Wardell formation (between the Sowerbyella and Hes- 
perorthis beds) in Tennessee: In the road cut north of Indian Creek on U. S. 
Highway 25E, Howard Quarter (T.V.A. 162-NW) Quadrangle. 
Discussion.—This species is suggestive of O. bifurcata because of the bifurcated 
costa in the brachial sulcus, but it differs in its more slender form and details of 
the ornamentation. 
OLIGORHYNCHIA INEXPECTATA Cooper, new species 
Plate 124, D, figures 24, 25 
Shell small for the genus, outline narrowly triangular with the pedicle valve 
having the greater depth. Sides nearly straight. Valves costate. 
Pedicle valve nearly flat in lateral profile but with the umbonal region slightly 
convex ; anterior profile narrowly convex; beak and umbo smooth; umbo and 
postmedian region carinate ; sulcus shallow, narrow and originating at about the 
valve middle; sulcus bounded by 2 strong subcarinate costae elevated above the 
flanks and forming a fold; sides marked by 2 oblique, narrow costae. 
Brachial valve gently and evenly convex in lateral profile; narrowly convex 
in anterior profile and with steep, precipitous sides; sulcus narrow at the pos- 
terior, originating at the umbo and extending to the anterior margin; sulcus wid- 
ening strongly at the middle and occupied by a single costa that originates at the 
middle; flanks narrowly rounded, marked by a bounding strong costa on each 
side of the fold and 2 finer costae on the sides. 
Measurements in mm.— 
Brachial Widest 
Length length Midwidth part Thickness 
Holotype (pedicle valve)........ 3.3 ? 1.8 2.2 1.1 
Paratype (brachial valve)....... ? 2.7 1.8 1.8 0.7 
Types.—Holotype: 117203a; figured paratype: 117203b. 
Horizon and locality.—Red Knobs formation (between the Athens cobbly beds 
and the marble) in Tennessee: On the roadside along Hiwassee River, 14 miles 
southeast of Charleston, Calhoun (T.V.A. 125-SW) Quadrangle. 
Discussion.—This species is characterized by its small and slender form, the 
short sulcus in the pedicle fold, and the narrow rib in the sulcus of the brachial 
