IK TEETH OF EARLY UNGULATES 205 



of forfcj-four teeth, the molars being of course bunodont, with the 

 three chief tubercles most developed. The bones of the tarsus 

 interlock and are not serial, as they are in many other members 

 of the Condylarthra. The astragalus has a shorter neck than in 

 Meniscothernom, for example. It has in this a likeness to the 

 same bone in the Amblypoda, to the primitive members of 

 which, such as Pantolamibda, this animal bears much resemblance. 

 " Astragali and many skeletal bones of Periptychus rhabdodon and 

 Pantolambda iathinodon are almost indistinguishable," observes 

 ilr. Matthew. The fore-feet of this genus are unknown, but it 

 would seem that it was plantigrade from the evidence of the hind- 

 feet. Tlaere are several species of the genus. 



Possibly, but not at all certainly, the Mioclaenidae, with the 

 genera Mioclaenus and Protoselene, are to be referred to this same 

 order of primitive Ungulates. It is only necessary to mention 

 them here, because they show very clearly the primitive form of 

 dentition of these early Eocene mammals. The teeth are quite 

 complete and unbroken by a diastema. The canines are but little 

 pronounced. The molars are not strictly tritubercular, but have a 

 prevailing trituberculy. The nature of the feet is not known. 

 Since the genus Protoselene, as its name denotes, shows an indica- 

 tion of a commencing selenodonty, it has been suggested that this 

 group is the stock whence the Artiodactyles have been derived. 



In any case, whether the particular comparisons that have been 

 made as to the relationship of various forms of Condylarthra are 

 valid or not, it seems to be plain that this group represents the 

 earliest Ungulate stock, but little differentiated from the con- 

 temporaneous Creodonts. 



Sub-Oedee 2. AMBLYPODA. 



This group of extinct mammals has the following principal 

 characteristics : — 



They are large, semiplantigrade Ungulates, of heavy build and 

 apparently elephantine gait. The dentition is for the most part 

 complete as in other ancient groups, and the canines are in the 

 later forms big tusks. The back teeth are brachyodont and 

 ridged (lophodont). Both radius and ulna in the fore-limb, and 

 tibia and fibula in the hind-limb, are well developed. The bones 



