HIPPARION. 



170 



the second and third of the right side, and the third, fourth and fifth of the left side. A series, exhibiting the triturat- 

 ing surfaces, from the second to the fifth inclusive, is represented in figures 20-23 [pi. XVIII]." (Gidley, 1007) Five 

 uppermolars of one individual; left m 1 , m 2 , p 4 , and right p 4 , p 3 . 

 Measurements (Gidley, 1007, p. 888) : 



transv 023 



" 022 



022 



019 



0215 



058 



Type figure. — Text Fig. 141 of this Memoir. 



Characters. — (Leidy, 1S69) (1) An animal of larger size than the type of Hippodon speciosum, about the size and 

 proportions of IHpparion occidentale or the existing Eqwus asinus. (2) Molars differing from those of H. occidentale in the 

 simple enamel plications, which are not more folded than in the horse. (Leidy, p. 286) Type a younger individual than 

 the type of occidentale, the molars comparatively little worn; nr not sufficiently worn to exhibit the inner enamel 

 plications. Internal enamel column [protocone] proportionately wider than in Hippodon speciosum and absolutely 

 wider than in IHpparion occidentale. (Matthew, 1013) (1) Protocone wide and flattened, oval from summit to base; 



(2) fossette borders with a few large plications, in little worn stage simple, with folds inconspicuous in half worn stage; 



(3) pli caballin persists in half worn teeth. 



Matthew refers to this species Amer. Mus. S3G2, a series of upper premolars and molars about half worn, from the 

 Republican River, Rawlins County, Kansas. 



Hipparion gratum Leidy 1860. 

 Plate 32.3. Text Figs. 142, 143. 



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

 Vol. VII, 1869, pp. 287-288, PI. xviii, fig. 25. 



Horizon and locality. — (Leidy) "... .in the Niobrara collection." Gidley remarks (1006, p. 146) "The type tooth, 

 with a few other isolated upper teeth, reported by Leidy from the Little White River locality, have hitherto represented 

 all that was known of this species." Name of collector not given. 



Type and paratype. — U. S. Nat. Mus. 587. (Leidy, Gidley, 1007, p. SS8) A right upper premolar, p 2 , associated 

 with two others, ?m 2 and m 3 . Measurements: (Type, Gidley, 1007) p 2 a.p. .0215, tr. .0175, height of partially worn crown 

 .031. 



Ncotypc. — (Gidley, 1007, p. 888) Amer. Mus. 10S63, anterior portion of a skull containing complete dentition of the 

 lef+ side, from the Nebraska formation, Upper Miocene, Little White River. 

 Type figure.— Text Fig. 142 (25, 26) of this Memoir. 



Characters. — Type. (Leidy, 1860) (1) Second superior premolar (fig. 25, pi. XVIII) closely resembles that of 

 Protokippus placidus in size, form, and proportions; (2) fossettes less gaping than in P. placidus; (3) enamel more plicate. 

 Type and ncotypc. (Gidley, 1007) (4) Protocone usually small, elliptical in cross section, separate from protoconule to 

 base of crown; (5) anterior border of prefossette plicated in the premolars, a character not observed in Protokippus. ((i) 

 Lachrymal and malar fossae moderately deep, limited in area; (7) anterior palatal foramina opening backward into long, 

 narrow slits, as in the modern horse; (S) palate strongly concave, especially anteriorly; (0) nasals short-tipped, but very 

 broad where they join the premaxillaries; (10) lower jaws short and deep as in P. placidus, but symphysis long and exten- 

 sion beyond premolars comparatively shorter; (11) angle of jaw proportionately smaller, lower border of ramus more 

 curved and bowed. 



Diameters of p 3 , anteropost 026 



" p 4 , " 025 



" m 1 , " 024 



" m 2 , " 0235 



" " m 2 , at middle of crown 0215 



Height of crown of m 2 (outside) 



