MAMMALIA. 



47 



mirabile from the Bridger Formation of Wyoming, presented 

 by Professor 0. C. Marsh, is mounted in a special Case 

 marked U. A plaster cast of a skull of Tinoceras ingens 

 (Fig. 37) is placed beneath it ; and a series of brain-casts 

 to show the relatively small size of its brain is arranged in 

 front. The skull bears three pairs of bony prominences, 

 which increase in size backwards, and seem to have been 

 covered merely with skin. These bony horns and the brain- 

 case are almost solid, with very few cavities. The upper 

 canine teeth are much enlarged, and are protected by long 

 flanges depending from the mandible. 



Pier-ease 



20. 

 Case IT. 



p I( j. 38. Skull and lower jaw of Arsinoitheriwm zitteli, from the Upper 



Eocene of the Fayum, Egypt ; one-twelfth nat. size. (Case S.) 



Arsirwitherium and its allies from the Upper Eocene of Pier-oase 

 the Fayum, Egypt, are technically Amblypoda, but their c ^ 8 

 precise affinities are still uncertain. A unique skull and 

 mandible (Fig. 38) is mounted in a special Case marked S, 



