WIELAND : THE OSTEOLOGY OF PROTOSTEGA 295 
relative shortening. But though a nearly complete carapace has recently been de- 
scribed,’ in the absence of further description of the Belgian material, now in process 
of elaboration by M. Dollo, we know very little of the limb development in this 
form, except byinference. In the case of Towxochelys, which is near to Lytoloma, we 
fortunately know the organization of the front flipper within close limits (cf. Fig. 
7), while I have but recently described the carapace of a most interesting new 
species, 7. Bawri."* In Toxochelys we find a markedly primitive form of flipper, in- 
deed the most primitive known, although the humeral contour and finger disparity 
indicate an animal capable of navigating the open seas. Also, the carapace of all 
the Toxochelyds known has very large fontanelles, suggesting a marine life quite as 
decidedly as the flipper; for though the laws of carapacial reduction are as yet only 
surmised, it is only in the marine members of the Cryptodira that prominent 
pleuro-marginal fontanelles occur. 
Because of the facts given it does, however, prove decidedly interesting to find 
that even in Protostega of the Upper Cretaceous, the hind limbs yet remain rela- 
tively long, though fully developed as flippers. For in Hretmochelys and Chelone as 
well as in Dermochelys, the fore flippers vary from about 1.55 to 1.60 times the length 
of the hind flippers; whilst in the orbicular bodied Protostega, with a tremendous 
spread of front flippers as already pointed out, this ratio falls to 1.30, which is, how- 
ever, a little in excess of Colpochelys. In the latter genus which has in some respects 
the most primitive flipper organization of any existing Cryptodiran the fore flippers 
are but 1.25 times the length of the hind flippers. Doubtless there are many 
further interesting numerical relationships not yet discovered. Though the rela- 
tively strong pattern and great size of both fore and hind flippers in Protostega and 
the related Archelon, taken with the broad body and shortness of the dorso-sacral 
series, may not indicate extreme and sustained swiftness, in conjunction with the 
cranial features these proportions do go far to confirm the opinion already expressed 
that these turtles, so powerfully equipped for both swimming and attack, may well 
have hunted actively swimming prey. The Protosteginee plainly included the larg- 
est and the most rapacious turtles which ever existed. 
"Wieland, ‘‘Structure of the Upper Cretaceous Turtles of New Jersey ; Lytoloma,’’ Am. Jour. Sci. September, 
1904. 
18 Wieland, ‘‘A New Niobrara Toxochelys,’? Am. Jour. Sci., November, 1905. 
