34: E. L. Troxell — New Species of Hyracodon. 



Osborn, H. F. 1890. The Mammalia of the Uinta basin. Pt. Ill, The 

 Perissodactyla. 'Trans. Amer. Philos. Soc, new ser., 16, 505-512, pi. 10. 



— 1893. The rise of the Mammalia in North America. This Journal (3), 

 46, 379-392, 448-466. 



— 1898. The extinct rhinoceroses. Mem. Amer. Mus. Nat. Hist., vol. 1, 

 75-164. 



Scott, W. B., and Osborn, H. F. 1882. Ortliocynodon, an animal related to 

 the rhinoceros, from the Bridger Eocene. This Journal (3), 24, 223- 

 225. 



— 1883. On the skull of the Eocene rhinoceros, Ortliocynodon, and the rela- 

 tion of this genus to other members of the group. Contrib. E. M. 

 Mus. Geol. and Arch., Princeton College, Bull. 3. 



— 1887. Preliminary account of the fossil mammals from the White River 

 formation, contained in the Museum of Comparative Zoology. Bull. 

 Mus. Comp. Zool., Harvard College, vol. 13, 151-171. 



Art. III. — NeiV' Species of Hyracodon; by Edward L. 



Troxell. 



[Contributions from the Othniel Charles Marsh Publication Fund, Peabody 

 Museum, Yale University, New Haven, Conn.] 



Introduction. 



Hyracodon, a genus of rhinoceros-like animals, is known 

 only in the Oligocene. Because of the slender limbs, long 

 neck, and relatively small skull, it was early characterized 

 by Scott and Osborn as cursorial, and it is probable that 

 these light-running ungulates held the place in the econ- 

 omy of nature now filled by the antelope and others of the 

 small ruminants. 



Because of the already great reduction of the lateral 

 toes, Hyracodon had reached a state of development 

 almost equal to that of Protohippus, and, the race persist- 

 ing, might well have become monodactylous, like the mod- 

 ern horse. 



Four species of Hyracodon have been made known, only 

 one of which has had figures accompanying the descrip- 

 tion. Leidy in 1850 gave us the first information of these 

 animals ;^ his later drawings (1852, 1854) have shown a 

 widely diversified group, therefore H. nehrascensis in its 

 broadest sense may apply to almost any hyracodont, and 

 the species is virtually synonymous with the genus. The 

 other known species are: //. arcidens Cope, H. major 

 Scott and Osborn, and f H. planiceps Scott and Osborn. 



