340 G. E. Wieland — On Marine Turtles. 



fact that as a merely web-footed turtle Toxochelys would have 

 been very unlike Amy da. For these percentual results must 

 always be considered in connection with the humeral changes 

 in the direction of marine forms, which are indicated in the 

 thalassoid humerus of Toxochelys, as well as the enlargement 

 of the pisiform to nearly the same size as in Eretmochelys. In 

 short, it is evident that Dr. Hay overlooked important factors 

 and that his views are untenable. 



When I originally described the flipper of Toxochelys I was 

 of the opinion that it represented the most primitive form yet 

 discovered that could be called more distinctly marine than 

 merely natatorial, long-fingered and web-footed ; and now that 

 I have had the present opportunity to briefly reconsider the 

 subject I may say that I believe this interpretation in accord 

 with the facts.* 



Dr. Hay " readily grants that the fore limb of Toxochelys 

 had entered on the early stages of those modifications which 

 resulted in the production of flippers." But as clearly enough 

 indicated by the facts, much more modification had been under- 

 gone, and the foot was more a swimming than a walking one. 

 Whether the third to fifth fingers were encased in a leathery 

 hide, or still retained some of their freedom of motion, as in 

 distinctly webbed types, is open to some question ; but never- 

 theless finger disparity, reduction of the 3d-5th claws, pisiform 

 enlargement and humeral change had all been accomplished to 

 such an advanced extent that the limb is to be regarded as a 

 flipper, quite admirably fitting Toxochelys latiremis to range 

 the great inland Niobrara Sea. And even were the anatomical 

 facts of less certain interpretation, the onus probandi would 

 rest on him who asserted the non- marine nature of those turtles 

 which occur so widely distributed in as extensive a chalk forma- 

 tion of indisputably marine origin as the .Niobrara Cretaceous. 



It is very evident, therefore, that on the basis of limb organ- 

 ization Toxochelys is a member of the Cheloniidse, and that as 

 proposed by the writer on the basis of the general organiza- 

 tion, limb structure, and relationships the genus is most con- 

 veniently placed in the Chelonidan sub-family Toxochelydinse. 



As a concluding word it may be added for the sake of clear- 

 ness that no great diagnostic significance is attached to the 

 presence of the epi-neural ossicles, — certainly not if they are 

 to be regarded as vestiges of a disappearing system, likewise 

 indicated in the genus Lytoloma of the Cheloninse. 



Yale Museum, New Haven, Conn., Sept. 26, 1905. 



*In view of the great interest of the subject I will as early as convenient 

 refigure the flipper of Toxochelys with all possible care. Dr. Hay is also of 

 the opinion that the great turtles of the Fort Pierre, and perforce the Nio- 

 brara Protostega were likewise littoral and web-footed rather than marine. 

 As will be incontestably demonstrated by the writer in a forthcoming 

 Memoir of the Carnegie Museum of Pittsburgh, Protostega and Archelon 

 were powerfully equipped for their marine habitat. 



