PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 289 
Measurements in mm.— 
Length Width Thickness 
PRGA cdrs'e 5 cca e os evo. o siegsie a 3.0. « ergs ea 9.3 10.8 4.0 
PatALy Pen LOO7O0d ) ose sc ce sc eleaee cceee wees 11.2 Ei7 4.7 
Types.—Holotype: 109785a; figured paratypes: 109758, 109767, 109783¢, 
109785e; unfigured paratypes: 109783a,b,d,e, 109785b-d, 109786a. 
Horizon and locality—Bromide formation (Pooleville member—Oxopflecia 
gouldi zone) in Oklahoma: Rock Crossing of Hickory Creek, about center sec. 
35, 1.5 S., R. 1 E., Carter County, Criner Hills ; (183 feet below massive lime- 
stone), second dam on Spring Creek, north of Woodford, Murray County. 
Discussion.—This species is suggestive of P. trentonensis (Hall) but differs 
in its strongly inflated anterior slope. 
PETROCRANIA ? MAGNA Cooper, new species 
Plate 25, B, figures 6, 7 
Shell very large for the genus, represented by brachial valve only, irregularly 
conical, broadly elliptical or crudely rectangular in outline, with the width about 
one-third greater than the length. Posterior margin nearly straight, lateral mar- 
gins gently rounded; anterior margin bilobed because of a slight emargination 
near the middle. Strongly convex in profile, with the greatest height at about 
the middle. Apex posterior in position and overhanging the short, steep posterior 
slope. Anterior profile moderately convex. Sulcus, shallow, extending from a 
point near the apex to the front margin where it forms a slight indentation. Sul- 
cus located to the left of valve center when apex is held away from the observer. 
Measurements in mm.—Holotype, length 20, width 26.5, height 7. 
Types.—Holotype: 109762. 
Horizon and locality —Effna formation in Virginia: Lower part of McNutt 
Quarry, 12 miles southwest of Bland, Burkes Garden (15’) Quadrangle. 
Discussion.—This species is not likely to be confused with any other known 
Middle Ordovician craniid because of its large size and peculiar form. As one 
of the earliest members of the genus, the great size is remarkable. 
PETROCRANIA PRONA (Raymond) 
Plate 25, F, figures 15-19 
Crania prona Raymonp, Ann. Carnegie Mus., vol. 3, p. 594, 1906. 
Petrocrania prona RayMonp, Ann. Carnegie Mus., vol. 7, No. 2, pl. 34, figs. 26-31, 1911. 
Not P. prona Raymond, Witiarp, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, 
p. 260, pl. 1, fig. 6, 1928. 
The shells from the quarry north of Luttrell identified as this species are in- 
correctly placed. It is a large species which cannot now be identified with any 
known species, but the material is inadequate to describe as new. 
Types.—Cotypes: Carnegie Mus. 5441-5443; figured hypotype: A.M.N.H. 
25046 
at 
