List of Casts, Models, and Photographs. 3 I 



13. Caenopus occidentalis {Leidy). 



Am. Mus. No. 1132. 



This characteristic Rhinoceros of the Middle OHgocene of the 

 West is ancestral to C. tridactylus of the Upper OHgocene, and 

 thus leads to the Dicerathere line. C. occidentalis was horn- 

 less, somewhat smaller than the living Sumatran Rhinoceros 

 and more lightly proportioned. This skeleton is mounted in 

 full relief. 



OsBORN, Mem. Am. Mus. Nat. Hist., I, Pt, III, April, 1898. 



14. Tylosaurus dyspelor {Cope). 



Am. Mus. No. 221. 

 Upper Cretaceous (Niobrara) of Kansas. 



Tylosaurus dyspelor was one of the largest of the Mosasaurs, 

 great marine lizards, distantly related to the living Monitor 

 Lizard (yaramis), but adapted to strictly aquatic life. This 

 fine skeleton, found by Mr. W. G. Bourne, is twenty-eight feet 

 long and exceptionally perfect, even the cartilages being pre- 

 served. The skeleton is mounted in the original matrix and 

 position. 



OsBORN, Mem. Am. Mus. Nat. Hist., I, Pt. IV, October, 1899. 

 15. Protoceras celer Marsh. 



Am. Mus. No 1236. 

 Upper OHgocene (White River, Protoceras Beds), S. Dakota. 



Protoceras was the largest of a group of Primitive Ruminants 

 found in the White River Beds, which had two toes in the 

 hind foot, four in the fore foot. The proportions are nearly 

 those of the smaller deer, but with shorter limbs and neck. 

 The male skull bore several bony bosses comparable to the 

 bosses on a giraffe skull instead of true horns or antlers; the 



