848 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
adductor field moderately large; adductor processes moderately developed. Four 
parallel pallial trunks extend anteriorly from the adductor field. 
Measurements in mm.—Holotype, length 18.2, brachial length 16.2, midwidth 
23.7, hinge width 20.0 ?, thickness 6.6. 
Types.—Holotype: 117639; figured paratypes: 117638, 117640. 
Horizon and locality.—Bromide formation (Mountain Lake member) in Okla- 
homa: In the road cut on Oklahoma Highway 18, 1.8 miles south of Sulphur, 
Murray County ; along the creek on the Fitz place, SE} sec. 27, T.2S., R.3 E,, 
14 miles west and # mile south of Nebo, Murray County ; in the Sowerbyites bed; 
150 feet below the top of the Bromide 0.1 mile down the hill from the Observa- 
tion Point on the Scenic Drive, 1 mile east of U. S. Highway 77, in the center 
NW4ANW43 sec. 29, T. 1 S., R. 2 E., Murray County. 
Discussion.—This species is a ieee one having a strong superficial resemblance 
to M. muralis. The chief differences are in the location of the greatest width of 
M. partita at or near the middle instead of near the hinge as in the Appa- 
lachian species. Differences appear in the interior also. The dental plates of 
M. muralis are the better and more fully developed, and the subperipheral rim 
of M. muralis is much more extravagantly developed than in the Oklahoma 
species. The latter also differs in the arrangement of the pallial trunks in the 
brachial valve, there being 4 in M. partita but only 2 in the other species. 
It is interesting to note that 7. partita was found in the reefy limestones south 
of Sulphur where it occurs with Sowerbyites. 
MURINELLA PARVA Cooper, new species 
Plate 217, B, figures 2, 3 
Shell small for the genus, wider than long and with the greatest width at 
about the middle; sides gently rounded; anterior margin broadly rounded; sur- 
face marked by alternating strong and fine costellae, about 3 or 4 to the milli- 
meter at the front margin and the stronger costellae separated by 2 to 4 costellae ; 
entire surface covered by strong concentric, elevated lines. 
Pedicle valve gently convex in lateral profile, broadly and moderately convex 
in anterior profile; umbonal and median regions swollen; anterior slope long 
and gentle ; lateral slopes moderately long and moderately steep. Interarea mod- 
erately long; pseudodeltidium large and strongly convex. 
Pedicle valve perceptibly concave in lateral profile ; broadly concave in anterior 
profile ; umbo concave. 
Measurements in mm.—Holotype, length 9.2, brachial length 8.3, midwidth 
11.4, hinge width 11.0, thickness 2.3. 
Type.—Holotype: 117643. 
Horizon and locality—Whistle Creek formation, in Lexington (15’) Quad- 
rangle, Virginia: On U. S. Highway 60, 100 yards southeast of Whistle Creek, 
2 miles northeast of Lexington; 14 miles northwest of Lexington. 
Discussion.—This is a small species of about the same size as M. plana. It 
differs from that species, however, in having a moderately concave brachial valve 
and finely cancellated ornamentation. | 
