1887.] 



387 



[Cope. 



Starting from Oreodon as the ancestral form, Eucrotaphus follows at a 

 little distance. The presence of the pollex observed by Scott in Oreodon 

 proves that it must be referred to a five-toed common ancestor with Dor- 

 catherium. The enlarged bulla? are added in Eucrotaphus, and the coos- 

 sified premaxillaries in Merycochcerus and Merychyus. The latter com- 

 mences the facial vacuities, which reach such huge proportions in 

 Leptauchenia and Cyclopidius. The loss of the incisor teeth from both 

 jaws, and diminished size, indicate that decadence is going on in Cyclo- 

 pidius, but the last term is reached in Pithecistes. Here not only incisors 

 but a premolar disappears. This family, once powerful in numbers, size 

 and strength, disappeared with the Upper Miocene period in North Amer- 

 ica. These relations may be thus displayed. A common ancestor with 

 Dorcatherium is assumed. This will be a genus like Protoreodon S. &0., 

 but without the caniniform inferior p. m. i of that genus, and probably 

 with the fifth crescent of the superior molars. Agriochcerus may have 

 been derived from the same, 



Pithecistes 



Coloreodon 



1 

 Agriochcerus 



Dichodon \ 



Cyclopidius 



I 

 Leptauchenia 



i 

 Merychyus 



1 

 Merycochcierus 



I 

 Eucrotaphus 



I 

 Oreodon 



(Tragulidae) 

 Dorcatherium 



