MERYCHIPPUS. 125 



suboval on premolars, more flattened on molars; (10) plications of enamel lake borders disappearing in well (two-thirds or 

 more) worn teeth; (11) pli caballin fold double, disappearing about one-fourth from base; (12) metastylid not separate 

 on po. (13) Lachrymal fossa apparently large; (14) malar fossa variable, not very deep. 



Matthew (1913) refers to this species a large series of upper and lower jaws and teeth from the Snake Creek beds 

 (Lower Pliocene) of Nebraska; also jaws and teeth from the Madison Valley, Montana, and from the Republican River 

 (Lower Pliocene) of Nebraska. 



Referred specimens are Amer. Mus. 13901a, 14001, 14003, 14014. 



Merychippus stylodus Merriam 1915. Nomen nudum. 



Merriam (letter, Oct. 29, 1915) considers that the species Merychippus stylodus should be eliminated as it appears to 

 represent quite closely the typical M . calamarius Cope. 



PLIAUCHENIA-PERACERAS ZONE. 14. LOWER PLIOCENE. 



This zone is believed to contain the last surviving members of the genus Merychippus, with which are 



FOUND PlIOHIPPUS, II IPPARION, HyPOHIPPUS, AND OTHER GENERA. 



Merychippus republicanus sp. nov. 



Plates 10.1, 17.7. Text Fig. 99. 



Horizon and locality. — Driftwood Creek, Republican River formation, Peraceras or Upper Procamelus zone, western 

 Nebraska. Early phase of Lower Pliocene. Type collected by W. Brous, 1879. 



