146 
Kirtley F. Mather 
One of the most common forms in all the horizons of the 
Morrow group is a Schizophoria undoubtedly conspecific with 
that figured and described by Cox. The collections include shells 
of all sizes from those with a length of less than 10 mm. to 
those more than 35 mm. long. Although there is considerable 
variation in outline, convexity, and strength of the sinus, it 
does not seem practicable to attempt either a varietal or spe- 
cific separation. 
In comparison with S. resupinata (Martin) of Great Britain 
and Europe, the American form seems to be more strongly 
convex and with more nearly equal length and width. Authentic 
specimens of the European species are conspicuously broader 
transversely. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Stations 136, 139, and 149). Brentwood 
limestone: near Fayetteville, Arkansas (Stations 134 and 135) ; 
Sawney Hollow, Oklahoma (Station 210). Kessler limestone: 
near Brentwood (Station 144) and on East Mountain, Fayette- 
ville (Station 209), Arkansas. Morrow formation: near Cho- 
teau (Stations 295, 302, and 306), Hulbert (Station 299), Ft. 
Gibson (Stations 301 and 303), and Gore (Station 304), Okla- 
homa. 
STROPHOMENID^ 
Genus ORTHOTETES Fischer 
Ortho tetes robust a (Hall) 
Plate IX, figures 2-3a. 
1858. Orthis robusta. Hall, Geol. Iowa, vol. 1, pt. 2, p. 713, pi. 28, figs. 
5a-d. 
Lower Coal Measures; St. Clair County, Illinois. 
1883. Streptorhynchus robustus. Hall, 2nd Rep. N. Y. State Geol., for 
1882, pi. (10) 40, figs. 12-16. 
Coal Measures : Illinois. 
1892. Derbya robusta. Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 10, 
figs. 12-17. 
Coal Measures: St. Clair County, Illinois. 
1892. Derbya robusta (?). Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 
IIB, figs. 7, 8. 
Upper Coal Measures: Winterset, Iowa; near Kansas City, 
Missouri. 
