2 1 8 Bulletin American Museum of Natural History. [Vol. XIX, 



It appears probable that this species and P. temnodon stand 

 in direct or almost direct genetic relationship to P. tnrgidus 

 and P. haydeni respectively. The occurrence of the species 

 of PalcBolagus is : 



{John Day Lepus ennisiauus 



f Leptauchenia Beds P. agapetillus P. intermedins 



White River } Oreodon Beds P. haydeni P. turgidus 



{. Titanotherium Beds P. temnodon P. hrachyodon 



The evolution in PalcBolagus ran in parallel lines in the dif- 

 ferent species, some being more progressive in one character, 

 some in another, but none exhibiting either wide divergence 

 or retrogression. The characters in which progress is ob- 

 served, as I have remarked in a previous paper, ^ are: 



1. Superposition of the Lepus tooth-pattern over the older 

 and simpler one inherited by PalcBolagus. This pattern, show- 

 ing at the crown in the older species, bites continually deeper 

 into the tooth until it entirely replaces the older pattern 

 during the whole life of the animal. 



2. Increase in length of teeth, molarization of anterior pre- 

 molars, and some reduction in size of m|. 



3. Bending down of facial portion of skull on cranial por- 

 tion. This is associated with lengthening of neck and legs. 



4. Increase in brain-capacity, in supra-orbital processes, etc. 



5. Increase in size. 



It will be observed that in the first and second characters, 

 our two species from the Titanotherium Beds are in all re- 

 spects more primitive than those of the Oreodon Beds. The 

 difference in size is trifling if any, the third and fourth charac- 

 ters cannot be observed in our specimens. 



PERISSODACTYLA. 



EQUID^. 



Mesohippus westoni Cope. 



Parts of upper and lower jaws, fore and hind feet, and 

 many fragmentary jaws and teeth represent one or more 

 species certainly distinct from M .hairdii,vfhxc\i does not occur 



' Bull. A. M. N. H., XVI, 1902, p. 306. 



