Fig. 8. Little tlirce-toed hortse (Mesohii)pNs hdinli) from the Middle Oligocene of South 

 Dakota. American Museum No. 1492 



Four-toed horse (Fjohippufi veniicolns) from the Lower Eoeene of Wvominfr. American 

 Museum No. 4S;i2 



18 



