PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 869 
portions gently concave to nearly flat. Interarea short, apsacline. Pseudo- 
deltidium not strongly arched. 
Brachial valve unevenly convex in lateral profile, the greatest convexity at 
about the middle. From the posterior margin the valve rises moderately steeply 
to the middle where it is abruptly rounded ; the anterior slope is moderately steep, 
somewhat less steep than the posterior slope and is flat in profile. Lateral slopes 
moderately steep. Umbo marked by a shallow, narrow sulcus equal in length to 
about a fifth the length of the valve. Cardinal extremities slightly deflected. In- 
terarea short. 
Interior of pedicle valve with a roundly elliptical to ovate muscle field having 
broad subflabellate diductor impressions and adductor impressions on a double 
median ridge located posterior to the middle of the field. Callosity posterior to 
muscle field not greatly thickened. Median ridge not extending anterior to the 
ends of the diductor impressions. Subperipheral ridge not strongly developed. 
Interior of brachial valve with moderately large cardinal process, small adductor 
field, and low and short median ridge. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Hielotype .Givitacveer tect. 23.0 22.4 28.8 25.9 4.6 
Paratype! (1176782) 62.8099. 2. 20.7 20.0 24.2 23.0 2.8 
3 (I7678h) soe Ssbks « 18.0 17.9 21.2 23.4 3.8 
a (Giizley(0) aan Boi 27.0 26.3 32.1 35.2 3.5 
‘ (QIZO7 5a) < dcjare si ctaets 41.4 40.7 52.0 50.4 ? 5.8 
bi (UT 7O7 7) cs snctisac cr 31.1 30.0 30.5 39.0 4.9 
Types.—Holotype: 117678b; figured paratypes: 117674a, 117675a, 117676, 
117677, 117678a,c,f,g; unfigured paratypes: 117675b, 117678d,e,h. 
Horizon and locality Lincolnshire formation (Hogskin member) in Ten- 
nessee: North of Hayes’ house, Evans Ferry, Howard Quarter (T.V.A. 
162-NW) Quadrangle; 0.1 mile north of the road, 0.8 mile southwest of Mount 
Eager Church, Powder Springs (T.V.A. 154-SW) Quadrangle; Sally Cleve- 
land Farm, 3 mile southwest of Washburn, Dutch Valley (T.V.A. 154-SE) 
Quadrangle ; 0.4 mile east-northeast of Red Hill, 4 miles west-southwest of Thorn 
Hill, Avondale (T.V.A. 162-SW) Quadrangle; 0.2 mile northwest up lane, 
4, mile southwest of Fleanor Mill, Powell Station (T.V.A. 137-SE Quadrangle ; 
southeast side of Library Hill, Dutch Valley (T.V.A. 154-SE) Quadrangle; 
2 miles southwest of Hall Crossroad, Fountain City (T.V.A. 146-SW) Quad- 
rangle; Beaver Creek, Maynardville (30’) Quadrangle. 
Discussion.—This species is characterized by its somewhat transverse form, 
which is unusual for the genus, and gentle profiles; it is thus in strong contrast 
to R. tennesseensis and R. subparallela. This species differs from FR. tennes- 
seensis in having its place of geniculation much nearer the brachial umbo, in the 
gentleness of the geniculation which forms a low, broad, rounded swelling, and 
in the low convexity and concavity of the valves. From R. subparallela the 
Hogskin species differs in having a more rectangular outline, less narrowly 
rounded anterior margin, more swollen umbonal and median region on the 
