Fauna of the Morrow Group 
187 
Remarks. This Spirifer, although belonging in the general 
group of camerati and presumably in the line of ancestry of S. 
eameratus itself, does not show any indication of the grouping 
of plications into fascicles which characterizes that species. It 
seems quite distinct from the other described members of the 
genus. 
A comparison may well be made between this form and the 
Spirifer from the Upper Carboniferous of Bolivia described by 
Kozlowski^o as S. condor. The latter is larger than S. goreii 
and has more numerous plications in the fold and sinus but pre- 
sents a similar outline and the same disappearance of the lateral 
plications near the cardinal extremities. The two forms are 
perhaps closely related. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Station 136). Kessler limestone: East 
Mountain, Fayetteville, Arkansas (Station 209). Morrow for- 
mation: near Gore, Oklahoma (Station 304). 
Genus BRACHYTHYRIS M’Coy 
Brachythyris laticosta n. sp. 
Plate XI, figures 16-1 6b. 
Description. Shell of medium size or a little larger, sub-cir- 
cular in outline, the greatest width near the mid-length of the 
shell, the hinge-line about one-third as great as the width, the 
cardinal extremities rounded. The dimensions of an average 
individual are : length, ±28.0 mm. ; width, ±27.0 mm. ; length of 
hinge-line, 10.2 mm.; thickness, ±14.0 mm. 
Pedicle valve most strongly convex posterior to the middle, 
the surface sloping abruptly from the umbonal region toward 
the cardinal margin and more gently toward the lateral and 
anterior margins, the valve not flattened toward the cardinal 
extremities; beak pointed, rather slender, and incurved; cardi- 
nal area short but high, concave, more strongly curved above 
near the beak than below toward the hinge-line, the large tri- 
angular delthyrium occupying the greater part of the area 
restricting the latter to two narrow lateral strips which are 
sharply defined from the convex cardinal slopes on either side; 
lateral slopes of the valve bearing, on either side of the mesial 
fold, from 8 to 10 broadly rounded, simple plications separated 
