202 



FOSSIL TURTLES OF NORTH AMERICA. 



A wholly similar humerus is contained in a small collection of hones sent the writer from 

 the University of Chicago. The few skeletal hones 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 maxillae extending back only to opposite the 

 choanae. 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 ischyros Wieland. 



Fig. 260. Archelon ischyros. Carapace with the entoplastron. XjTS. 



Archelon ischyros Wieland. 

 Figs. 260-268. 



Archelon ischyros, WlELAND, Amer. [our. Sci. (4), II, 1896, p. 399, plate vi, text-figs. 2-19; ibid., IX, 



1900, p. 237, plate ii, text-figs. 1-3, 6; ibid., XIV, 1902, p. 99, fig. 2; ibid., XV, 1905, p. 21 1, fig. I; 



Ann. Carnegie Mus., iv, 1906 (1907), p. 8, figs. 1, 4. Hay, Bibliog. and Cat. Foss. Vert. N. A., 



1902, p. 440. 

 Protostega ischyros, WlLLISTON, Univ. Geol. Surv. Kansas, II, 1897, p. 246. Wieland, Amer. Jour. 



Sci. (4), v, 1898, p. 15, plate ii, 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 



