276 S. W. Williston — Hind Limb of Protostega. 



Art. XXII. — On the Hind Limb of Protostega / by S. W. 



Williston. 



Although the structure of those huge Cretaceous turtles, 

 Protostega and Ai^chelon, has been, for the most part, deter- 

 mined in recent years through the researches of Baur, Hay, 

 Case and Wieland, little has hitherto been discovered con- 

 cerning the limbs, aside from the humerus and femur. In 

 examining the material of Protostega in the University of 

 Kansas museum recently, I found a nearly complete hind limb 

 collected by Mr. Charles Sternberg in the Kansas chalk two 

 years ago. This is of so much interest that I give herewith a 

 brief description and outline figure of it. The species is, I 



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Hind Limb of Protostega. 



suppose, P. gigas, though I do not feel certain. Among the 

 various specimens of this genus I have examined there is a 

 great difference in size, a character of doubtful value for specific 

 separation, as well as distinct differences in the shape of the 

 limb bones. The present specimen, for instance, is among the 

 largest discovered in the Kansas chalk, and has the femur 

 much more slender than in the specimen figured by Case 

 (Journal of Morphology, June, 1897, pi. vi, f. 18). 



The specimen had been, for the most part, washed from its 

 matrix, and the original relation of the different bones lost, 

 but since only the posterior part of the skeleton is present 

 they all clearly belong to the hind limb. The bones of the 

 fore limb, moreover, are all much larger than those of the 

 hind. Some of the phalanges were lost and probably one 

 of the tarsals. In the figure I have arranged the bones as 

 they would seem to belong, though very likely some of the 

 metatarsals and phalanges had different positions in the living 

 skeleton. 



For a review of the discussion as to the systematic position 

 of Protostega, the reader is referred to the paper by Professor 



