1000 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
the width; sides moderately rounded; anterior margin broadly rounded; an- 
terior commissure uniplicate to faintly sulcate. Surface fascicostellate ; costellae 
uneven in size, 3 or 4 in I mm. at the anterior margin; swollen costellae form- 
ing nucleus of poorly defined fascicles. 
Pedicle valve gently convex in lateral profile and with the maximum curvature 
just anterior to the umbo; anterior profile narrowly convex in the median region 
with long, moderately steep, flat lateral slopes. Beak slightly elongated ; inter- 
area curved, apsacline. Umbo subcarinate, the carination continued anteriorly 
nearly to the front margin as a low, narrow fold. 
Brachial valve somewhat more convex in lateral profile than the pedicle valve ; 
anterior profile gently and broadly convex and with a shallow median depres- 
sion. Region just anterior to umbo and median region moderately swollen. Sul- 
cus originating at the beak, narrow, moderately deep, continued as a narrow 
groove anteriorly to the front margin. Flanks gently swollen, slopes to the median 
sulcus long and gentle, lateral slopes gentle. 
Pedicle interior with short apical plate cemented to sides of dental plates and 
below delthyrial edge ; teeth small ; dental plates strong ; muscle field with elongate 
diductor scars and short adductor scars; median ridge faint. 
Brachial interior with long, strong brachiophore supporting plates; brachio- 
phores moderately long; cardinal process slender but nearly filling the narrow 
notothyrial cavity; median ridge low but extending into notothyrial cavity as 
a thickening. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Ficlotygent tis ss< o's oes 8.9 8.7 10.6 7.8 4.4 
Paratype (117305b).... 88 8.4 10.4 7.2 4.1 
‘% (117304b).... 9.6 8.9 10.1 6.4 4.6 
™ (117306a).... 10.7 10.1 T2a7 8.5 4.9 
. (rr7364e). 2 7.2 6.8 7.6 53 3.0 
Types.—Holotype: 117305a; figured paratypes: 117304a,d,e, 117305b, 
117306a, 117307a,b,d, 117308; unfigured paratypes: 117304b,c, 117306b, 
117307C,e. 
Horizon and locality—Bromide formation (Mountain Lake member) in Okla- 
homa: In the upper Io feet of the green shale (Platycystites bed) in the spill- 
way of the dam on Spring Creek, sec. 17, T. 2 S., R. 1 W., Murray County ; 
10 to 12 feet below the top of the purple and green shale in the cut on Oklahoma 
Highway 18, 1.8 miles south of Sulphur, Murray County; upper green shale 
(cystid bed) on west shore of Mountain Lake in E4 sec. 22, T. 2 S., R. 1 W., 
Carter County; 3 miles north-northeast of Springer; bed 13, 4 mile west of 
U. S. Highway 77, NW4 sec. 25, T.2 S., R. 1 E., Carter County; bed 10, same 
as preceding. 
Discussion.—This species is very similar to F. subcarinata but differs in a 
number of minor features. The Oklahoma shell has a deeper and more persistent 
sulcus, a narrower and longer carination on the pedicle valve, somewhat stronger 
