290 F-. B. Loomis — On Ticholeptus Rusticus and 



odon through some as yet unknown intermediate types. 

 Metoreodon is the last survivor of the great family and 

 continued until the middle of the Pliocene at least. 



Merycochoerus, originally described by Leidy and based 

 on jaws, has been the "catch all" for Miocene oreodonts. 

 In 1901 Douglass separated Promerycochcerus and Pro- 

 nomotherium from the mass of species described under 

 this generic name. Then Matthew described in detail the 

 type species M. proprius showing it to be a peculiar type 

 with short limbs and a shortened wide skull, in which the 

 nasals were very much reduced and the whole snout modi- 

 fied apparently by the development of a proboscis. So 

 far I have seen no other species which could be associated 

 with this one in this genus. Pronomotherium is the logi- 

 cal descendant of Merycochoerus with the snout still more 

 modified and the nasals so far reduced and moved back- 

 ward as to be actually behind the front of the orbits. The 

 tremendously deepened lower jaw and hypsodont teeth 

 make this type entirely distinct, and with it, this aberrant 

 line died out at the end of the Miocene. 



Another aberrant group which came off from Eporo- 

 edon and which was long associated with Merycochoerus 

 but which probably had less in common with Meryco- 

 choerus than with other genera is Pr ornery cochoerus, 

 large animals with very short limbs, a heavy elongated 

 body and a very heavy long skull, on which the zygomatic 

 arches are especially wide and thickened. Of this fully 

 described and illustrated genus no less than a dozen spe- 

 cies are known ranging from the upper part of the Upper 

 Oligocene through the Lower Miocene. One form, 

 P. montanus, has indeed been described. from the Middle 

 Miocene but it is desirable to have more complete material 

 of this species before being sure it belongs to this line. 



Merychyus is another genus to which many fragment- 

 ary species have been referred. Its type species is 

 M. elegans and with it belong several species, like M. ar en- 

 arum, M. minimus, M. liarrissonensis, M. leptorhyncus , all 

 small, light built types, with long slender limbs and tiny 

 hoofs so compressed laterally as to suggest the unguals 

 of deer and a very perfect digitigrade mode of locomotion. 

 Such species as M. medius and M. major are much heavier 

 built and when better known will, I am sure, be assigned 

 to other genera. In the case of M. medius some of my 

 material shows it clearly had stocky limbs, a moderately 

 heavy skull without an antorbital fenester, the whole 



