Tertiary Vertebrata of the West. 



467 



though some Oeodonts like Mesonyx have claws which are almost 

 hoofs in character. 



The Condylarthra comprise three families ; they are primitive 

 ungulates, with five-toed, plantigrade feet, with the astragalus like 

 that of the Creodonta and Carnivora, and have other characters known 

 only among TJnguiculates. The lowest representative of this group 

 is the Periptychidse. It comprises four genera. In Periptychus the 

 inferior premolar teeth have internal lobes, while in the other genera, 

 Anisonchus, ITemitJilteus, and JZaploconm, the internal lobes are want- 

 ing. The crowns of the true molars have seven tubercles ; the- 

 canines are of moderate size, and the inferior incisors small. 



Upper Jaw («). Mandible (b). Periptychus rhabclodon. 



Periptychus rhabdodon. 



The true molars in the mandible have four principal cusps, in 

 opposite pairs, with accessory median cusps in front and behind. The 

 angle of the lower jaw is not inflected, and the coronoid process 



