IX CEPA TOn TARE YUNG ULATES 205 
of forty-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 
Meniscotherium, tor example. It has in this a likeness to the 
same bone in the -Amblypoda, to the primitive members of 
which, such as Pantolambda, this animal bears much resemblance. 
“ Astragal and many skeletal bones of Periptychus rhabdodon and 
Pantolambda bathmodon are almost indistinguishable,” observes 
Mr. Matthew. The fore-feet of this genus are unknown, but it 
would seem that it was plantigrade from the evidence of the hind- 
feet. There 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 Uneulates. 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 1s 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-OrRDER 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-linb, are well developed. The bones 
