PART I CHAZYAN AND RELATED BRACHIOPODS—-COOPER 471 
variable, strongly elevated at its front margin. Brachial interior typical for the 
genus and family. 
Measurements in mm.— 
Brachial Hinge i 
Length length Midwidth width Thickness 
POM YOR Cochise ceri ceec est c ke es 15.2 15.5 18.9 16.5 11.6 
Paratype (pedicle valve 110662a).. 20.7 ? 25.3 23.0 6.1 
$ GRT7OSTH) ich fei ovideeie sis}. 6 11.3 11.7 15.1 13.8 7.7 
a (brachial valve 110669b). ? 20.1 25.1 22.5 6.3 
Types.—Holotype: 117037c; figured paratypes: 110662a, 110669b, 117037a-f, 
h-j; unfigured paratypes: 110662b,c, 110669a,c-i, 117037g; figured specimen: 
110063. 
Horizon and locality.—Bromide formation (Mountain Lake member) in Okla- 
homa: On Oklahoma Highway 99, zone 36, SW4NW4SW3 sec. 12, T. 1 N., 
R. 6 E., 3 miles south of Fittstown, Pontotoc County ; Decker’s zone 5, sec. 14a, 
about 2 miles southeast of McLish Ranch, near Bromide, Johnston County ; 
Mimella-bryozoan bed, 2,300 feet south and 2,000 feet west of the northeast cor- 
ner sec. 36, T. 1 S., R. 7 E., Johnston County; Decker’s bed 16, on West Branch 
of Sycamore Creek, sec. 22 and 27, T. 3 S., R. 4 E., Johnston County; top of 
bed 13, old road on hill northwest of old Galbraith Hotel, sec. 32, T. 1 S., R.8 E., 
Johnston County; Rock Crossing of Hickory Creek, approximately center sec. 
35, [.5 S., R. 1 E., Criner Hills, Carter County ; along creek 14 miles west and 
3 mile south of Nebo, SE# sec. 27, R. 2 S., T. 3 E., Murray County; road cut 
on Oklahoma Highway 18, 1.8 miles south of Sulphur, Murray County ; 30 feet 
above the Bromide sand in Spring Creek section, sec. 17, T. 2 S., R. 1 W., 
Murray County; bed 17, 266 feet below the top, sec. 22, T. 2 S., R. 3 E.,, 14 
miles west of Nebo, Murray County; Mimella zone, Baptist Grounds on Falls 
Creek, SWAiNW4iSWS3 sec. 33, T. 1 S., R. 2 E., Murray County; bed 22, road 
cut center N4 sec. 11, T. 2 S., R. 3 E., Murray County. 
Discussion.—This species is fairly common in the Mountain Lake member of 
the Bromide formation at a few localities. It is characterized by a moderately 
transverse form and a wide hinge which produces in many instances small ears 
or prominent cardinal extremities. The species as identified herein is variable 
and like other members of the genus includes narrow as well as wide forms. The 
wide-hinged forms are not like any species known from the Appalachian Valley 
region. They are also unlike any other Oklahoma species. The narrow forms 
which resemble M. subquadrata in outline and profile are more finely costellate. 
MIMELLA GILBERTI Cooper, new species 
Plate 128, A, figures 1-5 
Shell of about medium size for the genus, wider than long, hinge narrower 
than the maximum shell width which is located anterior to the middle; sides 
oblique, anterolateral extremities narrowly rounded; anterior margin broadly 
rounded ; anterior commissure fairly strongly uniplicate. Surface finely costate, 
about 46 costae along the front margin. 
