202 FOSSIL TURTLES OF NORTH AMERICA. 
A wholly similar humerus is contained in a small collection of bones sent the writer from 
the University of Chicago. The few skeletal bones accompanying it are not sufficient to 
identify the humerus as that of P. advena, but it seems probable that both it and the humerus 
in the American Museum belong here. 
Genus ARCHELON Wieland. 
Premaxillary beak more strongly developt than in Protostega. Crushing-surface of upper 
jaw mostly on the premaxillaries; that on the maxilla extending back only to opposite the 
choanz. Lower jaw with the rami not co-ossified at symphysis; at least, not until old age. 
Entoplastron T-shaped, with the anterior border concave from end to end. Radial process 
of humerus feeble. 
Type: Archelon tschyros Wieland. 
Fic. 260.—Archelon tschyros. Carapace with the entoplastron. zo. 
Archelon ischyros Wieland. 
Figs. 260-268. 
Archelon ischyros, W1ELAND, Amer. Jour. Sci. (4), 1, 1896, p. 399, plate vi, text-fgs. 2-19; ibid., 1x, 
1900, p. 237, plate ii, text-figs. 1-3, 6; ibid., xiv, 1902, p. 99, fig. 2; ibid., xv, 1903, p. 211, fig. 1; 
Ann. Carnegie Mus., tv, 1906 (1907), p. 8, figs. 1, 4.—Hay, Bibliog. and Cat. Foss. Vert. N. A., 
1902, p. 440. 
Protostega tschyros, Wituiston, Uniy. Geol. Surv. Kansas, 11, 1897, p. 246.—W1ELAND, Amer. Jour. 
Sci. (4), v, 1898, p. 15, plate il, text-figs. 1, 2. 
We owe our knowledge of this species to the study and the publications of Dr. G. R. 
Wieland. All the known specimens have been found by him near the South Fork of Cheyenne 
River in South Dakota, in the upper beds of that part of the Pierre formation that is below 
