200 
Kirtley F. Mather 
Immature individuals may be indistinguishable from the 
smaller specimens of C. wasatchensis but the specific characters 
ordinarily are apparent in those which have attained a length 
of 5 mm. Specimens of that size begin to show a lateral broad- 
ening and the initial development of the fold and sinus which 
distinguish them from specimens of C. tuasatchensis of the same 
size, although these somewhat indefinite characters would not 
serve to separate them from immature individuals of the three 
species mentioned in the preceding paragraph. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Stations 136, 137, and 139). Brentwood 
limestone: near Fayetteville (Stations 134, 135, 138, 147, 148, 
152, and 153), Brentwood (Station 145), and West Fork (Sta- 
tion 154) , ‘Arkansas ; Sawney Hollow, Oklahoma (Station 210). 
Kessler limestone: near Brentwood, Arkansas (Station 144). 
Morrow formation: near Wagoner (Station 294), Choteau (Sta- 
tions 297, 302, 306, and 307), Ft. Gibson (Stations 301 and 
303), and Gore (Stations 304 and 305), Oklahoma. 
Composita wasatchensis (White) 
Plate XIV, figures 7-lOb. 
1874. Rhynchonella Wasatchensis. White, Prelim. Rep. Inv. Foss., p. 19. 
Carboniferous (Coal Measures) : Wasatch Range, Utah. 
1877. Rhynchonella Wasatchensis. White, U. S. Geog. Surv. w. 100th 
Merid., vol. 4, p. 130, pi. 9, figs. 3a-d. 
Carboniferous: Rock Canyon, Wasatch Range, near Provo, Utah. 
Description. Shell small, sub-circular in outline, valves sub- 
equally convex, greatest thickness of shell posterior to the middle, 
fold and sinus absent or faintly developed. The dimensions of 
four typical individuals are: length, 12.5 mm., 9.1 mm., 6.3 mm., 
3.5 mm. ; width, 12.1 mm., 8.4 mm., 6.0 mm., 3.3 mm. ; thickness, 
7.0 mm., 4.7 mm., 3.6 mm., 2.1 mm. 
Pedicle valve most convex in and near the umbonal region, 
the surface curving abruptly toward the cardinal margin and 
more gently toward the lateral and anterior margins, the con- 
vexity decreasing anteriorly ; beak moderately arched and 
strongly incurved over beak of brachial valve, truncated by a 
comparatively large sub-circular foramen which encroaches upon 
the umbo ; mesial sinus absent or represented in some individuals 
