292 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Measurements in mm.—Holotype, diameter 14, height 3.5. 
Type.—Holotype: 109750. 
Horizon and locality—Red Knobs formation in Tennessee: 7 miles north- 
east of Charleston, Calhoun (T.V.A. 125-SW) Quadrangle. 
Discussion.—This species is characterized by its large size, circular outline, 
and its fairly high conical profile. Inasmuch as this is one of the earliest known 
species of the genus, its generally advanced form is exceptional. The specimen 
is as large as is commonly found in the Devonian, when species of this genus are 
abundant. It is larger than other Ordovician species and can be distinguished 
readily from Philhedra laclia and P. minor by this character as well as the very 
fine costellae. 
PHILHEDRA MINOR Cooper, new species 
Plate 26, EF, figures 12, 13 
Brachial valve small, slightly longer than wide, forming an eccentric cone. 
Apex smooth, located about one-fifth the length from the posterior margin, and 
overhanging the posterior slope. Anterior slope flattened, slightly inclined for 
half its length, but moderately steep and convex in its anterior half. Posterior 
margin nearly straight. Posterior slope steep and concave. Costellae nearly 
reaching the beak, increasing by implantation, threadlike and crowded at the front 
margin. 
Measurements in mm.—Holotype, length 6.6, width 4.2, height 2. 
Type.—Holotype: 109760. 
Horizon and locality.—Pierce formation in Tennessee: Pierce Mill, Walter- 
hill, 74 miles north of Murfreesboro. 
Discussion—This species suggests Philhedra laelia (Hall) but differs in its 
more elevated form and much finer ornamentation. It is a more elevated cone 
and with finer ornamentation than P. depressa. 
PHILHEDRA ? sp. 1 
Plate 22, H, figure 15 
This is the interior impression of a small species showing the characteristic 
pair of large muscles near the apex of the brachial valve. The specimen is 10.8 
mm. long and 8.7 mm. wide. Details of the exterior are unknown. 
Figured specimen.—109761. 
Horizon and locality.—Bromide formation (Mountain Lake member) in Okla- 
homa: Near the northeast corner NW} sec. 27, T. 1 S., R. 2 E., 3 miles north- 
west of Dougherty, Murray County. 
Subclass PYGOCAULIA 
Suborder ORTHOIDEA Schuchert and Cooper, 1932 
Superfamily OrTHACEA Walcott and Schuchert, 1908 
Family ORTHIDAE Woodward, 1852 
Progressive and terminal Orthacea with interareas on both valves; delthyrium 
open in most genera; pseudodeltidium rare ; muscle field of pedicle valve oval or 
