Cope. J 5U4: [Jan. 18, 



more inwards than the others, which it is supposed supported a nata- 

 tory web. In the Oreodontidse all the feet are regularly tetradactyle.* 

 The Anoplotheriidae differ also in the presence of an additional cusp on 

 the inner side of the superior molars, accompanied by an imperfect de- 

 velopment of one or both pairs of the internal crescents. In Anoplo- 

 therium the internal crescents of the inferior molars are incomplete, and 

 more or less represented by tubercles. In the Oreodontidce there are two 

 pairs of fully developed crescents, and no internal tubercles. The de- 

 tails of the structure express ' various affinities. The axis is intermediate 

 between that of the suilline and ruminant Artiodactyla ; the other cer- 

 vicals are suilline, while the remaining vertebrae are ruminant. The 

 scapula is ruminant, not suilline ; while the humerus is like nothing but 

 Anoplotherium. The radiocarpal articulation is intermediate between that 

 of hogs and ruminants. The unciform supports the lunar bone. The sac- 

 rum is ruminant, the ilium suilline. The femur and tarsus are much like 

 those of the peccary. 



The genera of this family known to me are the following : 



I. Orbit incomplete ; last premolars in both jaws with two external 

 ^crescents or Vs. 



Premolars three Coloreodon. 



Premolars four Agriochoerus. 



II. Orbit complete ; premolars four, the fourth with one external crescent, 

 a. No facial vacuities. 



Premaxillaries distinct ; otic bulla? not inflated. . .>. Oreodon. 



Premaxillaries distinct ; otic bullae inflated Eucrotaphus. 



Premaxillaries coossified ; otic bullae inflated Meryeochoerus. 



aa- Facial vacuities present. 



Premaxillaries coossified, dentigerous ; vacuities prelachrymal 



only. Merychyus. 



Incisors six above, persistent ; vacuities prelachrymal and pre- 

 frontal ; nasal bones much reduced Leptauchenia. 



Incisors very few, caducous ; vacuities very large Cyclopidius. 



III. Inferior premolars three. 



True inferior canine functional; inferior incisors one on each side. Plthecistes. 

 The number of species referred to these genera in the succeeding pages 



is as follows : 



Oreodon 3 



Eucrotaphus 3 



Merycochcerus 7 



Merychyus 6 



Leptauchenia 3 



Cyclopidius 2 



Pithecistes 3 



Agriochoerus 6 



Coloreodon 2 



35 



* I have observed this in the genera Oreodon, Eucrotaphus, Merycochcerus, 

 and Merychyus. 



