X.] EXTINCT MAMMALS. 373 



having the same number of teeth as the allied Tertiary European 

 family Adapidce, but all characterised by their more primitive 

 structural features. Indeed these early lemuroids appear to 

 present considerable resemblances to the creodont Carnivora, 

 and differ from all the other members of the sub-order to which 

 they belong by the great elongation of the bony symphysis con- 

 necting the two branches of the lower jaw at the chin. Several 

 other genera, in addition to the typical Chrtacis, are assigned 

 to this family. The second group is that of the Anaptomorphidce, 

 which is represented in the Puerco Eocene by a genus known as 

 Indrodon, and in somewhat higher beds by the typical Anapto- 

 morphus. Although in other respects coming closer to existing 

 types than is the case with the Chriacidcz, the present family is 

 broadly distinguished by the tritubercular structure of the upper 

 molar teeth. The third peculiar North American family of the 

 lemuroids is that of the Mixodectidcz, typically represented by 

 Mixodectes of the Puerco Eocene. 



Among the extinct creodont Carnivora there are two families 

 apparently restricted to the Tertiaries of North America, namely, 

 the Miacidce, and the Mesonychidcz, the former of which presents 

 such strongly marked affinities to the modern Carnivora that it 

 is frequently assigned to that group. The second family, on the 

 other hand, as represented typically by the genus Mesonyx of the 

 Uinta or lowest Oligocene, is characterised by the very simple 

 structure of the whole series of cheek-teeth, which are not unlike 

 the pre-molars of some of the higher carnivores. One of the 

 species of the typical genus attained dimensions as large as those 

 of a bear. In the widely distributed family Hyanodontida, an 

 exclusively North American genus is Patriofelis, which is regarded 

 as a specialised offshoot from Oxyana. 



Among the ungulates there are several extinct families con- 

 fined to North America. In the group forming a transition 

 between the pigs and the ruminants there is first of all the family 

 of the oreodonts (Cotylopida), which make their appearance in 

 the middle Oligocene, and continue to the Miocene and lower 

 Pliocene 1 . These ungulates, which were allied to the genus 



1 By American geologists the term Oligocene is not generally used, so that 

 the whole of the Tertiary strata are classed as Plistocene, Pliocene, Miocene, 



