1919] Merriam: Tertiary Mammalian Faunas of Mohave Desert 505 



The variations shown above between the large and small forms of 

 metapodials may well be comparable to the difference between Mery- 

 chippus intermontanus and M. sumani. 



Certain forms of foot structure seen in the Merychippus types of 

 the Barstow fauna might be transformed into those of horses in the 

 Kicardo, without extraordinary modifications. 



MERYCHIPPUS INTERMONTANUS Merriam 



Merychippus intermontanus, n. sp. Merriam, J. C, Univ. Calif. Publ., Bull. 

 Dept. Geol., vol. 9, pp. 50, 52, figs. 2, 3, 1915. 



Type specimen, no. 21400. An upper cheek-tooth dentition from locality 1401 

 in the Barstow Miocene of the Mohave Desert, California. 



Cheek-teeth large (figs. 36-39) ; crowns long, strongly curved, heavily cemented. 

 Protocone of upper cheek-teeth uniting early with protoconule. Enamel walls 

 bordering the fossettes comparatively simple. 



MERYCHIPPUS CALAMARIUS STYLODONTUS, n. var. 



Type specimen an upper cheek-tooth dentition, no. 21410, from locality 2057, 

 in the Barstow Miocene of the Mohave Desert, California. 



Upper cheek-tooth dentition (figs. 43-46) much as in typical Merychippus 

 calamarius (Cope). Crowns larger and relatively shorter than in M. sumani. 

 Protocone nearly circular in cross-section and often separate from protoconule 

 until the crown is reduced to a height measurement less than the width. Enamel 

 folds bordering the fossettes apparently simpler than in typical M. calamarius. 



MERYCHIPPUS SUMANI Merriam 



Merychippus, near calamarius. Merriam, J. C, Uuiv. Calif. Publ., Bull. 



Dept. Geol., vol. 6, p. 168, pi. 29, figs, la-lc, 1911. 

 Merychippus sumani, n. sp. Merriam, J. C, Univ. Calif. Publ., Bull. Dept. 



Geol., vol. 9, pp. 49, 50, fig. 1, 1915. 



Type specimen, no. 21422. Barstow Miocene, Mohave Desert, California. 



Upper cheek-teeth (fig. 41) much smaller than in typical Merychippus cala- 

 marius or in M. intermontanus. Crowns of cheek-teeth considerably elongated, 

 markedly curved, and well cemented ; height of the crowns often equal approx- 

 imately to twice their width. Protocone round, tending toward circular form in 

 cross-section, and discrete up to a stage of very advanced wear. Enamel bordering 

 the fossettes commonly more complicated than in any of the larger Merychippus 

 forms of the Barstow Miocene. 



PROTOHIPPUS? or PLIOHIPPUS?, sp. 



A single upper molar, no. 21423 (figs. 80 and 81), represents a 

 form apparently more advanced than the type of Merychippus inter- 

 montanus. It is closely allied to Protohippus, but better material 



