PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 275 
TREMATIS sp. 3 
Plate 19, C, figures 10, 11 
This third species is represented by a fragment of the brachial valve preserving 
the umbonal region and part of the right side. The species is characterized by 
its broad umbo, the strong convexity, and broad flat costellae separating rows 
of longitudinally elliptical pits. The specimen was taken from the base of the 
Lower Edinburg formation (Cyrtonotella zone) in Virginia: about 4 mile east 
of Strasburg Junction, Strasburg (15’) Quadrangle. 
Figured specimen.—109704. 
Genus SCHIZOCRANIA Hall and Whitfield, 1875 
SCHIZOCRANIA FILOSA (Halli) 
Plate 10, F, figures 20, 21 
Orbicula ? filosa Hatt, Pal. New York, vol. 1, p. 99, pl. 30, fig. 9, 1847. 
Schizocrania filosa Hall, BAsster, U. S. Nat. Mus. Bull. 92, p. 1144, 1915.—FoersTE, Bull. 
Sci. Lab., Denison Univ., vol. 19, No. 3, p. 202, 1920. 
This is a rare species in rocks older than the Trenton limestone, but it is re- 
ported as common by Foerste in the upper to feet of the Plattin group (Macy 
formation) or Barnhart formation of Ralls County, Mo., at several localities. One 
of Foerste’s specimens is figured which shows a number of individuals of different 
size attached to a pedicle valve of Rafinesquina cf. R. elongata. This early oc- 
currence of Schizocrania and Rafinesquina ss. leads to the suspicion that the 
top of the Plattin here is post-Black River in age and belongs to the Barnhart 
formation. 
Figured specimen.—to0g711. 
Family DISCINIDAE Gray, 1840 
Discinacea having a pedicle notch in early stages which is closed posteriorly 
by later growth to leave a more or less long slit partially closed by a listrium. 
Subfamily OrBICULOIDEINAE Schuchert, 1929 
Foramen encased in a long pedicle tube. 
Genus ORBICULOIDEA D’Orbigny, 1847 
Orbiculoidea pD’OrBIGNY, Compt. Rend. Acad. Sci. Paris, vol. 25, p. 260, 1847. 
ORBICULOIDEA EXIMIA Cooper, new species 
Plate 13, C, figure 5; plate 20, D, figures 11-23 
Shell fairly large, nearly circular in outline, biconical. Color shiny brown but 
often with a blue-gray tarnish. Pedicle valve forming a low cone with a sharp, 
nearly central apex directed slightly anteriorly. Slope anterior from the apex 
gently concave; posterior slope also gently concave but somewhat less steep than 
