112 



little. We can then safely conclude that the carapace of this turtle is more 

 elongate and narrowed than existing forms. Thus, in Chelone mydas, the 

 carapace is six-eighths as wide as long. 



It remains to discuss the question of the age of the specimen. It migkt 

 be objected that the absence of carapace, and the radiate character of the 

 margins of many of the bones, indicate that our type-specimen is young. To 

 this it may be replied, first, that it is in the (?) sternal bones unlike the j'oung 

 of any known type, when certain of their bodies do at all times exhibit 

 smooth margins as boundaries of the points of exit of the limbs ; moreover, 

 it is possible that these plates were dorsal ; secondly, the superior or inner 

 extension of the marginals exceeds that of any known tortoise in the adult 

 condition ; thirdly, the articular bone is ossified ; fourthly, separate ribs should 

 be discovered among extinct tortoises as an adult character, on theoretical 

 grounds, the more as it exists in one recent genus {Sphargis, fide Wagler). 



Distrihiition. — This fossil was found near 

 Fort Wallace, Western Kansas. It was entirely 

 recovered by excavating. The edges of one of 

 the large bony shields were seen projecting from 

 a bluff near Butte Creek, and was followed into 

 the chalk-rock with pickax and shovel with the re- 

 sult already indicated. The large bones were ex- 

 posed in an entire condition, but were mucii frac- 

 tured in the attempt to lift them from their bed. 

 Though carefully packed, the transport of fifteen 

 hundred miles still further injured them, and 

 the portions described were reconstructed of 

 over eight hundred pieces by myself. One of 



Fig. 3. — Costal bouos of a younc ,, , i, ii • , -, r\n • 



Testudopoiyphemm from heio^; nat- t^^ bouy plates was broken mto 108 pieces, 

 ""•"i"*^"- the ribs into 183, the marginals into 146, &c. 



A second species oi' Protostega^ appears to have existed during the Cretaceous 

 period, as indicated by a humerus from near Columbus, Miss., sent by Dr. 

 Spillman to the Academy of Natural Sciences. With it were received bones 

 of the mosasauroid Platecarpus tympaniticus. Cope; and Dr. Leidy, who 

 described them,^ regarded all as belonging to one animal. On this basis, he 



' Proceedings of the American Philosoiiliical Society for 1871, p. 173. 

 'Cretaceous Eei)tiles of North America, p. 42 : Smithsonian Contribntions, 18C4. 



