NO. 12 PERMIAN BRACHIOPODS FROM OREGON—COOPER 67 
lateral margins gently rounded, front margin emarginated. Pedicle 
valve having a prominent and deep sulcus originating 15 mm. surface 
measure anterior to the beak; sulcus narrow and deepening anteriorly, 
about 21 mm. long, surface measure. Anterolateral extremities nar- 
rowly rounded. Brachial valve nearly flat, with narrow and elongate 
beak; anterior profile broadly convex. Anterior margin flexed dor- 
sally to accommodate the short ventral tongue but no appreciable 
amount of folding takes place on the valve. 
Measurements in mm.—Holotype, length 21, length of brachial 
valve 18.7, width 15.2, thickness 10.8; paratype, U.S.N.M. 125413b, 
surface length 36, length of brachial valve 20, width 15?, thickness 
13. 
Types.—Holotype, U.S.N.M. 125413a; figured paratypes, U.S. 
N.M. 125413b, 125415. 
Localities —Pi2; S87, S103; U.O. 2202-2, 2204-3, 2205-5, 2216-2. 
Discussion.—This species is characterized by its flat brachial valve 
and anteriorly sulcate pedicle valve. The species most like it is D. 
prolongatum Girty but the Oregon species differs in having a much 
shorter sulcus in the pedicle valve and a flatter brachial valve. The 
sulcus in the Oregon species is deep only in the anterior third or 
quarter. 
DIELASMA RECTIMARGINATUM Cooper, new species 
Plate 12C, figures 27-31 
Shell of about usual size for the genus, narrowly elliptical in all 
profiles; maximum width anterior to the middle; anterolateral mar- 
gins broadly rounded; anterior margin truncated. Surface smooth. 
Anterior commissure faintly uniplicate, but no fold and sulcus defined. 
Pedicle valve slightly deeper than the brachial valve, gently convex 
in lateral and anterior profiles; median region gently inflated. 
Brachial valve gently convex in lateral profile, more strongly convex 
in anterior profile; beak small and acutely pointed ; umbo and median 
region gently inflated; anterior slope long and gentle; lateral slopes 
steep near the margins. 
Interior of pedicle valve with low median ridge extending from 
beak for three-fourths the length of the valve. 
Measurements in mm.—Holotype, length 19.6+, brachial length 
17.6, maximum width 16.3, thickness 13.0+. 
Type.—Holotype, U.S.N.M. 125414. 
Localities —L23; U.O. 2201-1. 
Discussion.—This species is characterized by the slender profiles, 
