PRELIMINARY KEY TO THE GEOLOGIC DISTRIBUTION OF THE PRINCIPAL SPECIES OF EQUIDiE. 



o 



o 



H 



m 



Ph 



L9 



Lower 



Upper 

 Middle 



o 

 o 



Ph 



Early 



Lower 

 Late 



Early 



18. 

 17. 



16, 



15. 



14, 



13, 



Transi- 

 tion 



Upper 



Equus Excelsus-Elbphas Imperator 

 Zone 



Loup River, Typical Equus excelsus 



Ashley River, redeposited Hipparion venustum 



Peace Creek, " H. princeps= Equus If raternus 



Pliohippus Proversus Zone 



Upper Etchegoin, Cal Pliohippus proversus 



Glyptotherium-Pliohippus simplict- 

 dens Zone 



Blanco, Tex Pliohippus simplicidens, etc. 



Ilingoceras-Pliohippus Zone 

 Thousand Creek, Nev. 



Rattlesnake, Oreg Pliohippus spectans 



Pliattchenia-Pliohippus Fairbanksi 

 Zone 



Lower Etchegoin, Cal Pliohippus coalingensis 



Ricardo (upper), Cal P. fairbanksi, Pliohippus tantalus 



Pliauchenia-Peraceras Zone 



Republican River, Kan Pliohippus nobilis, (?) Merychippus republicanus, Protohippus 



Devil's Gulch (upper), Nebr Hypohippus matthewi 



Alachua Clays, Fla Hipparion ingenuum 



Ricardo (lower), Cal mohavense callodonie, Pliohippus tantalus 



Snake Creek (upper), Nebr Pliohippus leidyanus 



Procamelus-Hipparion Zone 



Fort Niobrara, Nebr Pliohippus mirdbUis, P. pernix, P. supremus 



Little White River, So. Dak Parahippus 



P. cognatus 



Clarendon, Tex Protohippus 



P. perdihis, P. placidus, etc. 



Santa Fe Marls (upper) N. Mex. 



Santa Fe Marls (lower), N. Mex. . . .Merychippus calamarius 

 Snake Creek (lower), Nebr Merychippus calamarius, M. insignis 



Hipparion affine, Protohippus nio- 

 brarensis, H. whitneyi, etc. 



11. 



m 

 o 



Parahippus paumiensis, P. colora- 

 densis, Hypohippus osborni 



Archatohippus, Hypohippus 

 equinus, etc. 



O 

 O 



a 



Procamelus-Merychippus calama- 

 rius Zone 



Barstow, Cal., Temblor Merychippus surnani, M . intermontanus 



San Pablo, Cal. 



Temblor, Cal. (upper) Merychippus calif ornicus 



Late Middle 10. Merychippus sejunctus Zone 



Pawnee Creek, Col Merychippus paniensis, M. labrosus, M. 



Deep River, Mont. sejunctus, M. sphenodus, M. campestris 



Early Middle 9. Ticholeptus-Merychippus Zone 



Virgin Valley, Nev. ) 



Mascall, Ore. Primitive species of Merychippus, M. seversus, 



M. relictus, M. isonesus 

 Sheep Creek, Nebr. Parahippus avus, P. brevidens, P. gracilis 



Phillips Ranch, Cal. 

 Lower 8. Merycochcerus-Parahippus Zone 



Upper Harrison, Nebr Parahippus very abundant 



P. nebrascensis, P. tyleri, P. paumiensis, P. atavus, etc. 



Upper Rosebud, So. Dak. 

 7. Promerycochoerus-Miohippus Zone 



Lower Harrison, Nebr Miohippus gemmarosce, IKalobatippus ?Primitive species of Parahippus 



agatensis IP. pristinus, P. tyleri 



" Rosebud, So. Dak. 



Upper John Day, Ore Miohippus condoni, M. acutidens Kalobatippus prceslans 



Upper 6. Diceratherium-Miohippus Zone 



Middle John Day, Ore Miohippus anceps, M. equiceps, M. brachylophus, M. longicristis, M. primus, 



M. quartus 



5. Leptauchenia-Miohippus Zone Miohippus meteulophus 



= Protoceras Zone Miohippus brachystylus, M. intermedins, M. crassicuspis, M. validus, M. gidleyi 



Middle 4. Upper Oreodon Zone 



Brule, So. Dak Mesohippus eulophus 



3. Middle Oreodon Zone Mesohippus obliquidens 



= Metamynodon Zone Mesohippus trigonostylus 



2. Lower Oreodon Zone 



Brule, So. Dak Mesohippus, ? M. bairdii, ? M. exoletus, ? M. cuneatus 



Lower 1. Titanotherium-Mesohippus Zone 



Chadron, So. Dak Mesohippus celer 



Pipestone Creek, Mont Mesohippus westoni, M. latidens, M. montanensis 



Swift Current Creek, Assiniboia .... Primitive species of Mesohippus, M. pracocidens, etc. 



34 



