142 



osborn: OLIGOCENE, MIOCENE, PLIOCENE EQUINE. 



Characters. — (Cope, 1885, Osborn, 1917) (1) Of larger size than the type of Hipparion peninsvlatum; (2) protocone larger 

 and more prominent than hypocone, connected with protoconule and metaconule respectively; (3) crown of molar of 

 medium length, strongly curved inward; (4) grinding surface a little wider than long; (5) fossettes subtriangular, strongly 

 convex inward, each with one large and one smaller enamel fold; (6) external styles prominent. 



PLIAUCHENIA-PERACERAS-PLIOHIPPUS NOBILIS ZONE. 14. LOWER PLIOCENE. 



Typically exposed on the Republican River, western Kansas. 



Protohippus retrusus Cope 1889. 

 Text Fig. 114. 



Hippotherium relrusum Cope, Cope, Edw. D. "A Review of the North American Species of Hippotherium," Proc. Amer. Philos. 

 Soc, Vol. XXVI, 1889 (sig. dated June 5, 1889), p. 440, figs. 7, 7a, 8. 



Fig. 114. Type and paratype of Protohippus retrusus Cope. (7, 7a, S) Original type figures, Amer. Mus. Cope poll. 

 8350; (7, 8) crown view of m 1-2 , (7, 7a) crown and interior views of m 1 (inverted). After Cope, 1889. (Three middle 

 figures) Crown, external, and anterior views of the type tooth (No. S350), and (extreme right figures) crown and external 

 views of the more worn paratype tooth, redrawn by S. Oka. All figures natural size. 



Horizon and locality. — (Cope, 1889, p. 447) "From Phillips county, Kansas, from the Loup Fork bed." Probably 

 Republican River formation, Peraceras zone, late Miocene or early Pliocene. Type collected by Frank Hazard. 



Type.— Amer. Mus. Cope Coll. 8350. (Gidley, 1907) "Two upper molars." (Cope.) " This species is represented 

 in my collection by eight molars, two from one and six from another animal. These are associated with two superior 

 molars with somewhat different characters, which are intermediate between those of H. gratum and H. speciosum. All 

 were found in the same locality, but separated from their positions in the skull. The two molars [type] first above men- 

 tioned are about half worn, and present the characters of the species best." Measurements: (Cope) m 1 a. p. .019, tr. 

 .0185, height of crown .026; m 2 a. p. .020, tr. .018, height of crown, .036. 



