G. It. Wieland — Upper Cretaceous Turtles. 125 



most distinctive feature is the continuation of the articular 

 surface well out on to the fibular crest. The distal end, as in 

 the humerus, is facetted, not smooth. The characters of the 

 ulna and of the tibia, and the several phalanges present, are 

 in the main quite comparable feature by feature with these 

 several elements in Chelydra (see text figure 7). 



Of great interest is the form of the limbs. It is not to be 

 said off hand that Osteopygis had flippers, as is implied by 

 placing the genus in the Chelonidse, as has been done in the 

 American edition of Zittel's Handbuch. The limb bones 

 above made known are not entirely conclusive on this point. 

 The best study of the evidence at hand may be made from the 

 following tabular statement : — 



Chelydra. Osteopygis. Eretmochelys. 



Length of shell (26-) 74* (37') 



" humerus 6* 



" femur . ._ 6'4 



" ulna 3-5 



" 1st metatarsal 1*1 



Ratio to length of shell. 



humerus 4*3 



femur 4*0 



ulna 7*4 



1st metatarsal 23*6 



The larger the ratio the smaller the part, whence Osteopygis 

 Gibhi has a relatively shorter femur, humerus and ulna, with 

 a longer metatarsal than Chelydra. But the humerus is rela- 

 tively shorter than that of Eretmochelys, the femur relatively 

 much longer. Comparison of the metatarsal in Eretmochelys 

 cannot however be readily made since the hind flipper of the 

 latter is so very greatly reduced. The conclusion I am led to 

 is that the present species had by no means so well developed 

 flippers as I have shown the primitive sea turtle Toxochelys* 

 to have had. But as the phalanges had undergone some elon- 

 gation the toes must at least have been strongly webbed though 

 doubtless they yet retained their claws. The smooth distal 

 end of the humerus of the closely related Projpleura is con- 

 siderably more like that of the marine or natatorial types, and 

 may indicate that these forms were undergoing some adapta- 

 tion of the limbs for a pelagic or a littoral habitat. It would 

 however seem that the marine Chelonians destined to survive 

 were those which early acquired relatively powerful humeri, 

 and it is probable that a form with a long femur like Osteo- 

 pygis, even if the feet were fairly developed as flippers, was 



* Notes on the Cretaceous Turtles Toxochelys and Archelon with a classi- 

 fication of the Marine Testudinata. This Journal, vol. xiv, 1902, p. 95. 



74- 



(37- 



14-5 



8- 



ID- 



6- 



S' 



4* 



3-4 



1-4 



5-1 



4-6 



4-9 



6-1 



9'2 



9*2 



21-8 



26'4 



