PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 293 
obcordate ; ovarian impressions subreniform ; vascula media subparallel. Brachial 
valve with simple cardinal process, rodlike brachiophores, divergent and without 
other support than the shell substance of the notothyrial platform ; chilidial plates 
or chilidium rare. 
Subfamily OrtTHINAE Schuchert and Cooper, 1931 
Progressive Orthidae having short and curved interareas in the pedicle valve. 
Genus ARCHAEORTHIS Schuchert and Cooper, 1931 
Archaeorthis ScHUCHERT and Cooper, Amer, Journ. Sci., vol. 22, p. 243, 1931; Mem. Peabody 
Mus. Nat. Hist., vol. 4, pt. 1, p. 80, 1932—ULricu and Cooper, Geol. Soc. Amer. Special 
Pap. 13, p. OI, 1938. 
ARCHAEORTHIS BICONVEXA Cooper, new species 
Plate 31, B, figures 7-I0 
Shell of about usual size for the genus, wider than long; sides and anterior 
margin moderately rounded; hinge narrower than the midwidth which is the 
widest part; surface marked by strong, elevated, narrowly rounded costellae 
which increase by implantation and number 2 or 3 in a millimeter at the front 
margin. Costellae subfasciculate at the front margin. 
Pedicle valve strongly convex in lateral profile and with the maximum curva- 
ture on the umbo; anterior profile narrowly domed but with sides moderately 
sloping. Beak strongly incurved; umbo rounded and swollen; median region 
swollen nearly to the anterior margin to form a poorly defined fold. Sides mod- 
erately steep; anterior slope steep. Interior with large teeth having deep crural 
fossettes. Lateral plates developed along the delthyrial margin. Delthyrial cavity 
deep ; callosity anterior to muscle field short but extending to about the middle. 
Brachial valve moderately convex in lateral profile and with the maximum 
depth just posterior to the middle; anterior profile gently and broadly convex ; 
umbonal and postmedian regions swollen ; lateral slopes moderately steep toward 
the posterolateral extremities. Anterior slope gentle. Median sulcus poorly de- 
fined throughout its length, shallow. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness 
Holotype (pedicle valve) .......... 5.9 ? 7.4 5.8 2.0 
Paratype (brachial valve 116852b).. ? 4.8 5.9 4.0 i: 
Types.—Holotype: 116852a; figured paratype: 116852b. 
Horizon and locality—Limestone lens in the Womble shale in Oklahoma: 
1,100 feet south and 700 feet west of the NE. corner sec. 3, T. 2 N., R. 19 E., 
Pushmatahah County. 
Discussion.—This species is featured by its deep pedicle valve and a brachial 
valve with only a very shallow sulcus developed. In the latter respect it differs 
from all the Canadian Archaeorthis described by Ulrich and Cooper which have 
a well-marked brachial sulcus. 
