20<S 



FOSSIL TURTLES OF NORTH AMERICA. 



structure resembles that of the pelvis of the Cheloniidae, but it differs in having a median 

 bridge of bone connecting the pubes and the ischia. In this way ischio-pubic foramina are 

 formed, but they are of small size. As stated by Wieland, the extreme antero-posterior length 

 of the pelvis is 970 mm.; the extreme width, 810 mm. The fore-and-aft length of the pubis 

 is 460 mm. The length of the ilium is 300 mm., and its diameter, at the middle of the shaft, 

 is 105 mm. 



The femur (fig. 267, fern) has the ratio to the humerus that it has in Caretta caretta. Its 

 extreme length is 460 mm. The tibia (fig. 267, tib) has a length of 330 mm.; the fibula (fig. 267, 

 jib) a length of 310 mm. 



As in the case of Protostega, we can not doubt the adaptation of this turtle to marine 

 aquatic life. Its excursions on land must have been confined to those for the deposition of 



FlG. 268. Archelon ischyros. Pelvis seen from below. X /.1. 

 il, ilium; ip, ischio-pubic foramen; isch, ischium; pub, pubis. 



its eggs. We can only speculate as to what extent it spent its life on the high seas away from 

 the coasts. It seems probable that the broad and heavy body and the ponderous head were 

 obstacles in the way of sustained journeys over rough seas. Its prolonged beak, furnisht 

 with a broad crushing-surface, appears to indicate a diet, not of soft and actively swimming 

 animals, but of mollusks and crustaceans. Associated with the fossil were various genera ot 

 tetrabranchiate cephalopods, and the jaws of the turtle seem to have been admirably adapted 

 to pick up and crush such objects. 



Archelon marshi Wieland. 



Archelon marshii, Wieland, Amer. Jour. Sci. (4), ix, 1900, p. 248; ibid., xv, 1903, p. 215. Hay, 

 Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 440. 



This species was secured by Wieland in the upper beds of the Pierre formation, in South 

 Dakota, on the east side of the South Fork of the Cheyenne river. It is described in the 

 brief tst terms. The remains are stated to consist of the plastron, the humerus, ribs, and a 

 number of peripherals. These indicate a turtle about 11 feet in length. The humerus is 

 said to be rather straighter than that of A. ischyros and the plastron relatively more massive, 

 being fully one-half thicker than in the latter species. 



Family CHELONIID^: Gray. 



Thecophorous turtles fitted for life on the sea. Skull with temporal region extensively 

 rooft over. No nasal bones. No posterior palatine foramina. Quadrate notcht behind for 



