OLIGOCENE OF EUROPE^ NORTH AFRICA, AND NORTH AMERICA 189 



animal {Arretotherium) more or less similar to the last survivor (Merycopot- 

 amus) in the Miocene of India. 



Most interesting among artiodactyls is the newly arriving, small, and 

 primitive ruminant Gelocus, which appcuirs in the midst of this varied 

 browsing fauna, a representative of the family Gelocid», analogous to the 

 existing chevrotains, and a harbinger rather than ancestor of the varied 

 artiodactyl groups of later periods. 



The remainder of the mammal fauna of Ronzon may be partly described^ 

 in the language of Filhol (1881) as revealing to us an aquatic and riparian 



Fig. bl. — Hyiwioduiits, cuiuiuoii to Europe, Africa, and America. Skeleton of the Middle 

 Oligocene creodont Hyaenodon horridus of South Dakota. In the American Museum of Natu- 

 ral History. 



fauna with a few truly terrestrial animals, including also remains of birds, 

 reptiles, fish, insects, crustaceans, and molluscs. The insectivores are repre- 

 sented by primitive hedgehogs, the rodents by chinchilla-like Therido- 

 myidae, and the hamsters (Cricetodon) . The opossums (Didelphyidse) were 

 very small, and for the most part belonged to the Peratherium group, 

 which persists with little change from the Upper Eocene. The carnivores 

 are all small forms, excepting the creodont Hycenodon. No machiierodont 

 cats, or felids, have been discovered at this stage. The canid family is 

 varied, including Cynodoti, Cynodidis, and AmpMcynodon; the former, in 

 its rather spreading feet, long tail, and shape of the head, suggesting the 

 otter. We wonder at the absence of larger carnivores, for the ungulates 

 are worthy of stronger hunters than those which are known. The Mus- 

 telidae, or marten family, is represented by Proplesictis; the otter has not 

 been observed. 



