73 
Composita persinuata (Meek) 
1877. Athyris ? persinuata Meek, King’s U.S. Geol. Expl. 40th Par., 4, 
p. 81, Pl. 9, fig. 4. 
Remarks. Aside from the somewhat doubtful surface markings this 
form differs from Cleiothyridina incrassata (Hall) from the Lower Mississip- 
pi of the Mississippi valley in its smaller size, proportionally thicker shell, 
more abrupt deflexion of the frontal margin, and slightly less convex 
pedicle valve. Athyris monticola White from the Mississippian of Nevada 
has the median sinus extending almost to the beak and the greatest width 
of shell more anterior. Composita suhquadrata from the Upper Mississip- 
pian of the Mississippi valley has the pedicle valve much more convex in the 
umbonal region and the brachial valve more arched from beak to front. 
Judging from Meek's description and figures of his types of Composita 
persinuata our specimen differs in its less convex brachial valve, both 
longitudinally and transversely, the latter in Meek’s type meeting the 
opposite valve nearly at right angles; in outline and relation of length, 
breadth, and thickness they are similar, but our specimen is slightly 
smaller. We are inclined to think the Minnewanka form more closely 
resembles Meek’s species than any other with which we are acquainted. 
Locality and Horizon. In the Carboniferous of Nevada, in the Minne- 
wanka region in the Lower Mississippian of section 2-23 (R). 
Composita ozarkana Mather 
1915. Composita ozarkana Mather, Bull. Sci. Lab. Denison Univ., vol. 18, 
p. 198, PI. 13, figs. 11-15 c. 
Remarks. It seems desirable to separate this large, broad form from 
Hall’s species of Composita trinuclea ; in the Minnewanka section the typical 
small, narrow form was not observed. Mather founded his species C. 
ozarkana upon this difference and as the Minnewanka specimens appar- 
ently agree in all essential respects with his species they are placed within 
it. From C. suhquadrata (Hall) from the Chester it differs in its somewhat 
smaller size, in the more flat-topped fold of the brachial valve, and in the 
presence of the lateral sinuses in the pedicle valve. From C. subtilita 
(Hall) from the Pennsylvanian it may be differentiated by its less elongate 
form, by the lower median fold of its brachial valve, the more shallow median 
sinus of the pedicle valve with its slighter anterior extension as well as in 
the presence of the lateral sinuses upon this valve. 
Locality and Horizon. Basal Pennsylvanian of Arkansas and Okla- 
homa. In the Minnewanka region in the Pennsylvanian of section 2-11 
(o), -13 (c). 
Composita subtilita (Hall) 
1852. Terebratula subtilita Hall, Stansbury’s Exped. Great Salt Lake, 
p. 409, PI. 2, figs. 1 a, b, 2 a, b; T. ? subtilita Davidson, 1857, Mon. 
British Carb. Brach., Pal. Soc., p. 18, PI. 1, figs. 21, 22; T. subtilita 
Hall, 1858, Geol. Surv., Iowa, vol. 1, pt. 2, p. 714; Spirigera sub- 
tilita White, 1875, U.S. Geog. Geol. Surv., W. 100th Mer., Rept., 
