188 FOSSIL TURTLES OF NORTH AMERICA. 
Cope was the first to refer the bone to the turtles, and he placed it in his genus Protostega. 
At a little later time Leidy referred it to Atlantochelys. In 1889 Baur correctly concluded 
that it could belong to neither Protostega nor to . Atlantochelys, but he did not name the genus. 
Thistvassesenvedde Wiclandicotonn 1900. 
The total length of the humerus (fig. 244) 1s 10 inches, or 253 mm. ‘The shaft, where 
narrowest, is 48 mm. wide and 28 mm. thick. The distance from the extremity of the ulnar 
process to that of the radial process was estimated to be 152 mm. The breadth of the distal 
end is 93 mm.; the thickness, 30 mm. The form of the bone is shown by the figure, copied 
from Leidy. 
Genus ATLANTOCHELYS Agassiz. 
A genus based on the proximal end of a humerus of a sea-turtle. The head and the ulnar 
and radial processes in approximately the same plane. Radial process hardly separated from 
the head. Ulnar process directed nearly parallel with axis of bone. Shaft unusually slender. 
Type: Atlantochelys mortont Agassiz. 
Fic. 244.—Neptunochelys tuberosa. Fic. 245.—Atlantochelys mortont. Portion of humerus 
Humerus forming the type. »}. forming the type. +. After Leidy. 
Atlantochelys mortoni Agassiz. 
Fig. 245. 
Atlantochelys mortont, AGassiz, Proc. Acad. Nat. Sci. Phila. 1849, p. 169 (no description); in Lripy, 
Smithson. Contrib. Knowl., xiv, art. vi, 1865, p. 43.—Leipy, Ext. Vert. Fauna West. Terrs., 
1872, p. 342.—WIELAND, Ree Jour. Sci. (4), 1900, p. 419, figs. 14-16.—Hay, Amer. Nafuralise 
XXXII, 1898, p- 930; Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 440. 
Misacaurus mitchell, Leipy, Smithson. Contrib. Knowl., xiv, art. vi, 1865, 43, 117, plate vil, figs. 3-5 
Protostega neptunta, Cork, Fifth Ann. Report U. 5. Geol. Surv. Terrs., 1871 (1872), p. 334; Proc. Amer. 
Philos. Soc., x11, 1872, p. 433; Vert. Cret. Form. West, 1875, p. 257. 
Like Neptunochelys tuberosa, this species is based on a humerus which was derived from 
the Upper Cretaceous formation. The exact locality and level were not reported, but we 
know that the fossil was found in one of the beds of Cretaceous greensand in Burlington 
County, New Jersey. 
Of this humerus (fig. 245) there was secured only the proximal half or less. This fragment 
had a length of about 280 mm. The shaft was extremely slender, being 73 mm. mide and 
60 mm. thick. The ulnar process rises above the head about 75mm. The radial process is 
