PLATE 10 



PREORBITAL FOSSAE IN MERYCHIPPUS. 



COMPARISON OF SKULLS IN THREE SPECIES. 



All figures one-half natural size. 



Driftwood Creek, Nebr. Lower Pliocene 1. 



Pawnee Creek, North- Middle Miocene 2. 



eastern Colorado 

 Deep River, Mont. " " 3. 



Mascall, John Day Basin, " " 4. 



Ore. 



Merychippus republicanus Osborn, type, Am. Mus. 8347. This 

 is the skull figured by Cope under the name Hippotherium 

 speciosum Leidy. Lachrymal fossa shallow, obscure; no 

 malar fossa. 



M. sphenodus Cope, referred specimen, Am. Mus. 9390. Lachry- 

 mal fossa deep, constricted; no malar fossa. 



M. isoncsus var., referred specimen, Am. Mus. S105. Lachrymal 

 fossa deep, extensive; malar fossa obscurely separated. 



M. isoncsus Cope, type, Am. Mus. 8175. Lachrymal fossa deep, 

 extensive; malar fossa obscurely separated. 



