150 



osborn: OLIGOCENE, MIOCENE, PLIOCENE EQUID.E. 



this species, consists of a fragment of the upper jaw of an adult individual, containing the back four molars, which are so 

 far worn as to be inserted by fangs. (Measurements:) The four teeth occupy a space of three and one-third inches in length 

 and an inch in breadth." Also Am. Mus. 10840. 

 Type figure. — Text Fig. 117 of this Memoir. 



Characters. — (Leidy, 1S58) (1) "... a deep depression or lachrymal fossa in advance of the orbit, as in the deer, 

 Oreodon, etc." (Leidy, 1869, p. 294, Osborn, 1918) (2) Deciduous premolars provided with cement; (3) enamel fold- 

 ings around the fossettes as simple as in the horse; (4) protocones conoid, continuous with protoconule; (5) protocone and 

 hypocone on the same longitudinal plane and of equal size; (6) a pli caballin and single enamel fold entering the pre- and 

 postfossettes from metaloph in m 1 ; (7) enamel of dp 3-4 more ptychoid. Leidy's fuller description of his Pliohippus 

 (Mcrychippus) mirabilis type is contained in his discussion of the genus Merychippus (1869, pp. 292-296). 



Pliohippus supremus Leidy 1869. 



Plates 25.11, 26.2, 31.3,4. Text Figs. 118, 119. 



Protohippus supremus, Leidy, Joseph. "The Extinct Mammalian Fauna of Dakota and Nebraska," Jour. Acad. Nat. Sci. Phila. (2) 

 Vol. VII, 1869, p. 328, type, PI. xxvii, figs. 3, 4; neotype, Matthew, W. D., and Gidley, J. W. "New or Little Known Mammals from 

 the Miocene of South Dakota," Bull. Amer. Mus. Nat. Hist. Vol. XXII, Art. VIII, May 26, 1906, p. 143, figs. 8, 9. 



Fig. 119. Original figures of neotype (Gidley) of Pliohippus supremus Leidy, Amer. Mus. 10844, skull of young 

 individual with milk premolars, dp 2 - 4 . (Upper) Side view of skull, fig. 8, p. 143 ; (lower) neotype right maxillary with milk 

 premolars, fig. 9, p. 144. la. fs., lachrymal fossa, ma. fs., malar fossa. Both figures one-half natural size. After Gidley, 

 1906. 



Horizon an d locality— (Leidy, 1869, p. 326.) "...discovered on Little White River." Upper Miocene. Type 

 collected by F. V. Hayden, 1866. Neotype from same locality. 



Type and Cotype.— Acad. Nat. Sci. Phila. Coll. (casts Amer. Mus. 10776-7). (Leidy) Two superior molars of the left 

 side, belonging to two different individuals in different stages of wear, of which Gidley selected that represented in Leidy's 



