294 MEMOIRS OF THE CARNEGIE MUSEUM 
further detailed comparison with Protostega. The writer has, however, pointed out 
the fact that the littoral, or semi-marine, turtles of the Cretaceous of New Jersey, 
especially Osteopygis and Lytoloma, present many interesting primitive features, 
amongst these being relatively longer hind limbs, the inference being a quite clear 
one, that in the evolution of the limbs of the marine turtles, in correlation with cara- 
pacial and other changes, the hind limbs underwent shortening, and the front limbs 
a compensatory elongation. In fact in Osteopygis, a form now known to be very 
closely related to the ancestors of the Chelonine, the femur is distinctly longer than 
Fic. 8. Colpochelys Kempii Garman. >< 3 Fore and hind flipper of a specimen in the United States National 
Museum (ratio of fore to hind flipper, 1.25). : 
Fore Flipper. H, humerus with ectepicondylar perforation set well in from the anterior border: R, radius in 
natural position revolved somewhat beneath the ulna (U) ; r, radiale, bounded by the radius, the intermedium and first 
carpale ; 7, intermedium, wu, ulnare; p, pisiform ; c, centrale bounded by the intermedium, ulnare, and first to fourth 
earpalia; I., V., first and fifth fingers. 
Hind Flipper. 7, tibia, F, fibula; L., V., first and fifth toes. The tibia and fibula support a single heel or astrag- 
alo-calcaneal element, (a) theoretically formed by the fusion of four elements corresponding to the radiale, intermedium, 
ulnare, and centrale. The first toe is borne on tarsale I., the second on tarsale II., and the third to fifth on tarsalia IIT.— 
V., fused. Metatarsal 1 (m) is the exact equivalent of metacarpal 1, and metatarsal V. has a pisiformoid development. 
the humerus, as is also the case in Chelydra, a tortoise which is in many respects sug- 
gestive of specialization in some direction similar to that doubtless followed by the 
direct ancestors of the marine turtles. In Lytoloma, an upper Cretaceous and lower 
Eocene genus closely related to Chelone, the femur appears to have undergone some 
