E. L. Troxell — Homed Eocene Ungulates. 



31 



Art. IV. — Horned Eocene Ungidates; by Edward L. 



Troxell. 



[Contributions from the Othniel Charles Marsh Publication Fund, Peabody 

 Museum, Yale University, New Haven, Conn.] 



Iii the Eocene period two distinct forms of rhinoceros- 

 like animals are fonnd to have rugose and thickened 

 nasal bones which appear to be the beginning of horn 

 supports analogous to those of our modern rhinoceros. 

 The first of these is the well known Colonoceras agrestis 

 Marsh; the second is Metahyrachyus bicornutus, new 

 genus and species. 



In Oligocene time we see nothing again of horned 

 rhinoceroses until late in the period, when the dicera- 

 theres come in, and one concludes therefore that we 

 either have no record of the intervening members of one 

 single, great, and continuous race, or that the earlier 

 branch was cut off and that nature wrought the later 

 forms from another, a hornless group leading through 

 Trigonias Lucas and Ccenopus Cope. 



Colonoceras agrestis Marsh. 



(Figs. 1-3.) 

 Holotype, Cat. No. 11082, Y. P. M. Eocene (Bridger), near Fort Bridger, 

 Wyoming. 



11082 TYPE 



Y. P. M. 



Fig. 1. — Colonoceras agrestis Marsh. A small specimen closely related to 

 Hyrachyus, but having rugosities on the nasals. Eocene (Bridger). X 1 /^- 



The original description of this species is as follows : ] 



1 O. C. Marsh, This Journal (3), 5, 407, 1873. 



