410 G. R. Wieland — Archelon ischyros. 



Fibula. — The fibula is a much smaller bone than the tibia 

 proximally, but nearly of the same size distally. The proximal 

 extremity is subquadrilateral in outline with the long side turned 

 to the tibia. Just beneath the articular face in the outer side 

 there is a broad longitudinal scallop. Distally the bone 

 expands, and the articular face is somewhat convex, and ellipti- 

 cal in outline, with a notch for the articulation with the tibia. 

 These two bones have some resemblance to the tibia and fibula 

 of Protosjphargis. 



Dimensions. 



The very great width of Archelon as compared with either 

 Protostega or Protosjphargis will have been noticed. The ribs 

 in the middle dorsal region are quite exactly 1°^ in length ; add- 

 ing IS*^™ as the approximate width of the centra, and 12^°" as the 

 additional width due to the marginals, assuming them to have 

 been present, we obtain a total width of 2*25" ; that is of more 

 than 2™ after making full allowance for dorsal curvature, which 

 must have been slight. If proportioned then as in Thalasso- 

 chelys caretta the total length would be 11 feet. From the 

 vertebral column the same length is indicated. From the five 

 cervical vertebrae the average length would seem to be 9*^". 

 These vertebrae must have supported an enormous head, so that 

 •60^^™ is certainly the lowest cranial length that can be assigned. 

 The caudal vertebrae are estimated at '70^™ ; that is : 



M. 

 Cranial length _ _ _ '60 



Eight cervical vertebrae *72 



Ten dorsal " 1-35 



Three sacral " '15 



Eighteen (?) caudal vertebrae '70 



3-52 or 11 ft. 4 in. 



This latter will no doubt be a very little less than the actual 

 length. 



The most striking feature of this huge animal was formed 

 by the massive forearms, which had a spread of from 16 to 20 

 feet. Had they had the proportions of Thalassochelys the 

 distance would be 20 feet. But there is a wide difference in 

 the structure of the two arms, and I favor the lower estimate. 



The length of body I assign to ischyros is considerably less 

 than that first estimated for Protostega by Prof. Cope and later 

 by Hay on the basis of the hypo- and hyoplastron,^ notwith- 

 standing the great disparity in skeletal weight. While it is 

 scarcely permissible to make calculations based so entirely 



* Field Columbian Museum Publication 7, Chicago. 



