ee! OF 
NO. 12 PERMIAN BRACHIOPODS FROM OREGON—COOPER 51 
Surface marked by 10 to 11 rounded costae separated by spaces 
narrower than the costae; sulcus marked by 4 costae, the median 2 
of which extend to the umbo and the other 2 intercalated outside the 
median costae and appearing at about the middle or slightly posterior 
to the middle; fold marked by 5 costae, the 3 median ones strong 
and extending to the umbo, the 2 outside ones appearing on the sides 
of the outer 2 strong median costae but not extending posterior to 
the middle. Flanks marked by 2 or 3 costae. 
Ornamentation in addition to costae consisting of wide and wrinkled 
frills extending laterally for fully 7 mm. on each side of the valve and 
for an undetermined distance anteriorly. 
Pedicle valve gently convex with the greatest convexity located in 
the umbonal region. Beak strongly incurved ; sulcus originating about 
one-third the length from the umbo, shallow throughout but becom- 
ing very wide anteriorly and occupying slightly less than two-thirds 
the valve width at the front. Tongue moderately long, truncated 
anteriorly. Flanks narrow, flattened anteriorly but with steep slopes 
and rounded sides posteriorly. 
Brachial valve moderately convex in lateral profile and more 
strongly convex in anterior profile; maximum convexity slightly 
posterior to the middle. Umbonal region gently convex; fold orig- 
inating about one-third the length anterior to the umbo, low, grad- 
ually widening but occupying only half the width at the front margin. 
Flanks narrowly rounded and with steep slopes to the margins. 
Measurements in mm. 
Width 
Brachial with 
Length length Width frill Thickness 
IRI@ WTA a ao On BOE Oeics Oke 11.8 10.6 14.5 ? 8.0 
Paratype (125370) 6. 255.803 12.2 11.0 15.0 20.6 2 
Patabypen(la5377 aa. o.hvecec 12.5 TreT 16.4 ? 8.0 
Types.—Holotype, U.S.N.M. 125378; figured paratypes, U.S.N.M. 
125377; 125379, 125380. 
Localities —638 ; L8; P10; S14, S20, S40, S41, S46, S50; U.O. 
2201-4, 2204-1, 2204-3. 
Discussion.—This subspecies is represented by 4 specimens, all of 
them approximately of the same size, about one-half inch in width. 
Small size is the chief distinction between the Russian species S. 
mutabile and its American subspecies. A comparison of Tscherny- 
schew’s figures of S. mutabile of comparable size (Tschernyschew, 
1902, pl. 45, figs. 2 and 4) shows the development of the costae in 
