G. JR. Wieland — On Marine Turtles. 125 



retain a strong pedestal affording a powerful and firm type of 

 muscular insertion. Curiously enough, the earlier Niobrara 

 Protostega was better provided in this respect, since its radial 

 crest forms a distinct ala nearly as prominent as that seen in 

 Dermochelys. 



This failure of Archelon to develop or retain, as the case may 

 be, a prominent crest with stronger type of radial musculature 

 may indeed indicate a certain failure to progress in swimming 

 power and in resultant ability to follow the southward retreat 

 of the great central Pierre sea. In fact, it was at just about 

 this period of culmination in size of the Protostegidse that the 

 Dermochelan line more successfully accomplished such a 

 change, as shown by the Eocene Psephophorus, a turtle nearly 

 approaching Archelon in size and having a strongly pronounced 

 and very low-set radial crest. It is on such grounds, as much 

 as by the possible destruction of the eggs of the young by 

 marine or even by newly evolved mammalian enemies, that suffi- 

 cient cause is surmised for the extinction of these most gigantic 

 of all marine Testudinates. 



The Pelvic Girdle and Pes (figure 9). — The very perfect 

 and uncrushed pelvis of the type was accompanied by the left 

 femur, tibia, fibula, tarsals, and nearly all the metatarsals. On 

 the right side, the femur is also present, with the proximal two- 

 thirds of both tibia and fibula, which end in obliquely bitten 

 off but healed surfaces. Both the femur and those mutilated 

 elements are lighter and several centimeters shorter than the 

 corresponding bones of the left side. In short, the evidence 

 is conclusive and unmistakable that this animal had its right 

 flipper bitten off when still young, and that as a result of this 

 injury the remaining portion of the flipper was more or less 

 arrested in growth by disuse. Such accidents are now and,' then 

 noted in fossils. The type of Dromocyon vorax shows a broken 

 lower jaw, subsequently reknitted, which was doubtless received 

 in some raid on the young of Palmosyops, while a large per- 

 centage of existing marine turtles have had their flippers more 

 or less mutilated by predaceous fishes and sharks. 



I need not remind those familiar with the Testudinate osteol- 

 ogy that the tarsal region of the sea-turtles is decidedly more 

 variable in its organization than is the carpal region. Owing 

 to this cause and to the failure to identify the excellently con- 

 served tarsals with those of the crushed elements of Protostega 

 gigas, it has not proved possible to orient the tarsals except in 

 the most provisional manner. They are all free and heavy 

 bones, and there is little doubt that all were present on the left 

 side, however difficult and uncertain exact orientation may be. 



The metatarsals are more readily recognizable, the fifth be- 

 ing much flattened and highly characteristic. Its distal half 



