PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER SII 
Horizon and locality—Edinburg formation (Cyrtonotella zone) in Virginia: 
Ravine on south side railroad, 4 mile west of Strasburg, Strasburg (15’) Quad- 
rangle. 
Botetourt formation in Virginia: Junction Virginia Highways 731 and 724, 
2 miles northwest of Brownsburg, Lexington (15’) Quadrangle. 
Discussion.—This species is placed in Eoplectodonta with a query because no 
denticles were seen along the hinge in any of the specimens studied. Although 
the hinge seems to be edentate, the other characters, internal and external, seem 
to be those of Eoplectodonta. On the outside the ornamentation with its large 
costellae separating broad bands of fine radii and the prominent wrinkling along 
the posterior margin are all characteristic features of Eoplectodonta. On the 
inside of the brachial valve prominent development of the median septum is 
characteristic although the development of the muscle callosities and the nar- 
rowed, elevated front are not carried to the extent that is usual in geologically 
younger species. 
Eoplectodonta ? dubia differs from E. foerstei and E. alternata in having less 
robust and convex valves and in lacking hinge denticulations. 
EOPLECTODONTA FOERSTEI Cooper, new species 
Plate 209, A, figures 1-3 
Shell moderately large, wider than long with the length equal to about two- 
thirds the width. Cardinal extremities acute and mucronate in the young but 
rounded and obtuse in large adults. Lateral margins of adult gently rounded ; 
anterior margin broadly rounded. Surface marked by costellae of several sizes. 
In the half-grown stage the ornamentation consists of costellae of 3 sizes, the 
larger costellae standing out prominently and producing a slight plication of the 
valve and separated by about 1o of the finer costellae. Among the finer costellae 
occurs an occasional costella of intermediate size. In the adult half of the shell 
costellae of the stronger and intermediate sizes predominate and are separated 
by 1 to 4 finer costellae. In the young half of the valve strong oblique wrinkles, 
about 8 on each side of the hinge, are conspicuous. These are not carried on in 
the later growth stages and are thus confined to the young half of the valve. 
Fine concentric growth fila complete the ornamentation. 
Pedicle valve only gently convex in the young and with a fairly prominent 
low fold in the posterior half. Lateral profile of the adult strongly convex with 
the greatest convexity in the posterior third. Anterior profile of adult forming 
a very convex arch with steeply sloping sides. Fold of the young stages lost 
before the middle of an adult. Anterior half of an adult somewhat tumid and 
with moderately steep slopes to the margins. Slopes to cardinal extremities con- 
cave and steep. Cardinal extremities deflected toward the pedicle valve. Beak 
small, protruding slightly beyond the posterior margin. Interarea slightly curved 
and orthocline in position. About 14 denticles are visible on one side of the 
hinge of No. 110992c, but this may not be the full complement because this side 
of the valve is broken. 
