G. R. Wielamd — Archelon ischyros. 411 



upon relations obtaining in different genera, I do think that 

 when a complete skeleton of Protostega is once obtained 

 it will be found to lack considerable of the enormous length 

 which has been assigned to it. The cervical vertebra figured 

 by Cope is of much the same size as in Protosjphargis. Also, 

 as Cope found ten ribs, he must have had at least one approach- 

 ing the longest in length. From comparison of this kind 

 including Sphargis itself, Protostega gigas must have been 

 less than three meters in length. 



Systematic. 



In attempting to place the relationship of Archelon in exist- 

 ing classifications we are faced by some very heterogeneous 

 characters. 



From the characters which have been given I think it will 

 be accepted that the fossil under consideration stands more 

 nearly on the border line between the two cryptodire divisions 

 than any form yet described. The endoskeleton strongly 

 resembles that of Protostega and Protosphargis^ while a con- 

 nection, though slight, between carapace and endoskeleton 

 points to the Chelonidw. I cannot pass the strong likeness of 

 the shoulder girdle, nor the great similarity in the vertebrae. 

 I would define Protosphargis, Protostega^ and Archelon as the 

 gigantic Upper Cretaceous representatives of three genera of 

 the DermochelydidcB with the approach to the ChelonidcB in 

 the order named. 



Occurrence. 



Archelon ischyros was obtained near the South Fork of the 

 Cheyenne River, about 35 miles southeast of the Black Hills 

 in the uppermost Fort Pierre or ]^o. 4 of the Upper Cretaceous. 

 The skeleton lay deeply imbedded at the side of a small ravine, 

 extending out from the base of a butte of typical Miocene. It 

 had formed the nucleus of a lenslike mass of very hard marl. 

 The excavation of the ravine had no doubt broken down the 

 portion containing the head and right forearm but a year or 

 two since. At the time of interment the skeleton may have been 

 subjected to the action of strong currents, coming from the 

 direction in which it headed, as would be indicated by the 

 fragmentary marginals near the head, the absence of smaller 

 bones, phalanges and caudal vertebrge, except somewhat 

 to the rear and beneath, and furthermore to the fact that 

 the third and fourth (?) cervical vertebrae, with their articu- 

 lating neural arches, were lodged between the carapace and 

 plastron just against the coracoid full two feet out of their 



