(ill 



osborn: OLIGOCENE, MIOCENE, pliocene equid^e. 



Referred specimens from the same horizon: upper jaws, Amer. Mus. 12914, 12917c, 12917c! ; lower jaws with teeth, 

 Amer. Mus. 12913, 12916, 12917e, 12919, 12920. 



Type figure. — Plate 3.6, text Fig. 45 of this Memoir. 



Characters. — (Matthew, 1913, Osborn, 1918) (1) The type is an animal of slightly smaller size than the type of 

 Mesohippus bairdii, more progressive in dentition and in foot construction. (2) Teeth slightly more hypsodont than in 

 M. bairdii; (3) p 2 ~ 4 occupy more space (.036) than m 1-3 (.031); (4) m 3 considerably reduced; (5) parastyle of p 2 prominent, 

 elongating; (6) metaloph nearly uniting with ectolophs of molars, also uniting in an early stage in the premolars; (7) 

 hypostyle relatively large on premolars and molars; (8) lower teeth in referred specimens with metaconid and metastylid 

 cusps relatively large and distinct; (9) metalophid united with metastylid in an early stage of wear. 



In the paratype referred lower jaw, Amer. Mus. 12920, with various parts of hind foot, we observe: (10) 

 median metatarsal larger than in M. bairdii; (11) shafts of lateral metatarsals relatively smaller; (12) Mts. Ill with 

 a small, oblique articulation of cuboid. Also in the juvenile upper jaws, Amer. Mus. 12917c, 12917d, (14) the milk 

 premolars agree in crown pattern with the permanent premolars but the transverse width is less, and (15) both in the milk 

 and permanent premolars metalophs unite with ectolophs at an early stage of wear. 



This species of dwarf horse, which may be known as Miohippus equinanus, should be compared with Cope's dwarf 



Mioh ippus equinanus 



A/o. /29/2 y-u/se 



A A7. 



Fig. 45. Miohippus equinanus Osborn, Amer. Mus. 12912, superior molar-premolar series of the type, p x -m 3 of the 

 left side. Natural size. 



horse from the John Day, M. longicristis, the type of which is unfortunately lost. The referred lower jaws are much 

 smaller than the cotype of M. longicristis. Although the type and all the referred specimens are of smaller size than the 

 type of Mesohippus bairdii from the Oreodon zone of the Middle Oligocene, these animals are more progressive in denti- 

 tion and in foot structure; in some respects they are so progressive as to present an approximation toward the dental 

 type of Parahippus (Matthew, 1915). 



Miohippus gemmarosae, sp. nov. 

 Plates 3.7, 4.1,2,3,4,9. Text Figs. 46, 47. 



Horizon and locality. — From the Lower Rosebud formation, Promerycochcerus zone, Bear-in-Lodge Creek, Pine Ridge, 

 South Dakota. Type collected by Paul Miller, American Museum Expedition of 1907. 



Type — Amer. Mus. 13808. Upper teeth and skull fragments. Measurements: p 1-4 .062; m 1 a. p. .016, tr. .0214; 

 in 2 .016. Referred specimens, or paratypes, all from Lower Rosebud, Pine Ridge, South Dakota, upper and lower jaw 



