PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 291 
details are not clearly shown. The valve is also indefinite in shape, and the apex 
is not discernible. The large muscle scars in the rear of the shell are not clear 
but strongly suggest Petrocrania. The unusual feature of the valve is the low 
and short median septum. This may be a freak of silicification but seems to be 
a part of the valve. 
PETROCRANIA sp. 3 
Plate 25, G, figures 20-22 
This is a small species or possibly the young of a larger one. The outline is 
somewhat trapezoidal. The largest specimen measures 7.2 mm. long, 7.7 mm. 
at the widest part which is well anterior to the middle, and nearly 4 mm. high. 
The apex is about three-fourths the length posterior to the front margin. 
Figured specimens.—109766a,b. 
Horizon and locality—Bromide formation (Mountain Lake member) in Okla- 
homa: From a deep well on the Jones Farm, sec. 22, T. 5 N., R. 3 E., Potta- 
watomie County. 
Genus PHILHEDRA Koken, 1889 
Philhedra Koxen, Neues Jahrb. Mineral., Geol. and Paleont., Beil., Bd. 6, p. 465, 18809. 
PHILHEDRA DEPRESSA Cooper, new species 
Plate 26, B, figures 4, 5 
Shell of a brachial valve of about medium size for the genus, nearly circular 
in outline and forming a low cone in lateral profile. Lateral margins gently 
rounded but anterior margin more strongly rounded and posterior margin nearly 
straight. Apex located two-fifths the length from the posterior margin. Beak 
and umbo smooth; beak directed posteriorly. Anterior slope only moderately 
steep and gently convex in profile. Posterior slope long and flattened just pos- 
terior to the apex, moderately steep. Lateral slopes slightly convex. Surface 
marked by distant strongly elevated costellae, 2 or 3 in the space of 1 mm. at the 
front margin. The apex is located 4 mm. anterior to the posterior line. 
Measurements in mm.—Holotype, length 10.2, width 10, thickness 2.2. 
Type.—Holotype : 109749. 
Horizon and locality—Prosser formation in Wisconsin: 25 feet above base of 
the Duck Creek Quarry, near Green Bay. 
Discussion.—This species is distinguished from Philhedra laelia by its more 
nearly central beak and more distant costellae. 
PHILHEDRA FERRUGINEA Cooper, new species 
Plate 26, C, figures 6-8 
Brachial valve circular in outline and forming a low cone with the apex 
slightly posterior to the center. Anterior slope slightly convex and gentle; pos- 
terior slope flat in profile, shorter and steeper than the anterior slope. Surface 
marked by numerous fine costellae 4 or 5 in a millimeter at the periphery. Apex 
located about 6 mm. anterior to the posterior margin. 
