644 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
than a right angle. Fold marked by 7 costae and the sulcus by 6 costae; flanks 
marked by 9 costae. 
Pedicle valve gently convex in lateral profile, broadly and gently convex in 
anterior profile ; sulcus shallow and wide, occupying about half the width; flanks 
gently rounded and moderately steep. 
Brachial valve gently convex in lateral profile and with the greatest convexity 
at about the middle; anterior profile broadly rounded but only moderately con- 
vex; fold low, noticeably elevated at the front; flanks rounded and moderately 
steep. 
Measurements in mm.—Holotype, length 7.8, brachial length 6.9, width 8.3, 
thickness 4.5. 
Types.—Holotype: 117223a; unfigured paratype: 117223b. 
Horizon and locality Bromide formation (Pooleville member) in Oklahoma: 
On Spring Creek, sec. 17, T. 2 S., R. 1 W., Murray County. 
Discussion.—This species is characterized by its small size, numerous costae 
on the fold and sulcus, and length and width nearly equal. The species is sug- 
gestive of FR. pristina in size but has more numerous costae. It differs in the 
same respects from R. orientalis, R. basalaris, and R. raymondi. 
ROSTRICELLULA PLATTINENSIS (Fenton) 
Plate 132, H, figures 43-51 
Protorhyncha plattinensis Fenton, Amer. Midland Nat., vol. 11, p. 135, pl. 3, figs. 21-24, 1928. 
A small variable species originally assigned to Protorhyncha, to which genus 
it does not belong. Specimens from the type locality show the characteristic 
median septum and rostral chamber without a cardinal process of Rostricellula. 
The whole habit of the species is that of the latter genus rather than Protorhyncha 
or the new genus Ancistrorhyncha. Specimens of the latter occur with R. plat- 
tinensis but could not be confused with it as they are ornamented by fine 
costae or costellae and are without a median septum. The serial sections figured 
by Fenton (pl. 4, figs. 1-6) do not conform either to Rostricellula or Ancistro- 
rhyncha. 
Measurements in mm.—Hypotype (111491), length 10.5, brachial length 9.5, 
width 11.3, thickness 7.1. 
Type.—Figured hypotype: 111491. 
Horizon and locality—Plattin group (lower) in Missouri: On the J. Heck 
place, 14 miles south-southeast of River Aux Vasses, Weingarten (15’) Quad- 
rangle. 
Discussion—The narrowly rounded fold of this species is its chief character- 
istic. The 2 median costae of the fold are elevated above the 2 lateral ones, thus 
producing a narrowly rounded fold when viewed in anterior profile. In this re- 
spect it is somewhat like R. acutiplicata, but that species is wider, differently 
ornamented, and with different proportions to the valves. 
