PLIOHIPPUS. 



151 



fig. 4 as the type. Measurements : (Leidy) external length of crown 22-26 lines. Gidley selected the molar represented 

 in plate XXVII, Fig. 4, as the type (1907, p. 889), regarding it as m 1 or m 2 , and recording the following measurements: 

 m 1 a.p. .024 tr. .025, height of crown .048. He selected as a neotype (1907, pp. 889-890) Amer. Mus. 10S44, a considerable 

 portion of a juvenile skull and lower jaws containing the milk teeth dp 2 " 4 , m 1 . 

 Type figure. — Text Fig. 118 of this Memoir. 



Characters. — (Leidy, 1869, p. 328, Osborn, 191S) (1) Superior molar teeth bear a resemblance to those of Proto- 

 hippvs perditus; (2) protocone isolated in the unworn crown (Fig. 4); (3) protocone early connected by wear with proto- 

 conule; (4) prominent, simple enamel folds entering pre- and postfossettes from median portion of metaloph; (5) a pli 

 caballin and prominent enamel fold entering prefossette from crochet region; (0) protocone of elongate-oval section, 

 projecting farther inward than hypocone. (Characters based on neotype, Gidley, 1907, p. 890) (7) Size considerably 

 exceeding that of Pliohippus mirabilis. (8) Deciduous premolars of narrower proportions than in P. mirabilis; (9) greater 

 complexity of the enamel foldings in both the milk and permanent series. (10) Malar fossa without dividing ridge, com- 

 paratively smaller and more shallow than in P. mirabilis; (11) basisphenoid proportionately longer than in Protohippus 

 perditus, not overlapped by vomer. (Matthew, 1913, from type and neotype) (12) Deciduous premolars decidedly more 

 hypsodont than in Pliohippus mirabilis; (13) permanent molars with long crowns; (14) protocone united with protoloph 

 except near summit of crown; (15) protocone united with hypocone when teeth are well worn; (16) protocone oval, rather 

 large, anterior in position on premolars; (17) fossette borders with a few enamel folds, disappearing when tooth is about 

 half worn; (18) pli caballin well developed toward the summit of crown. 



Referred specimens are Amer. Mus. 10844, 10848. 



Pliohippus per nix Marsh 1874. 



Plates 25.12, 28.1. Text Figs. 120, 121, 122. 



Pliohippus pemix, gen. et sp. nov., Marsh, O. C. "Notice of New Equine Mammals from the Tertiary Formation," Amer. Jour. 

 Sci. and Arts, (3) Vol. VII, No. 39, Mar. 1874, pp. 252-253, no figure. 



Horizon and locality. — (Marsh, 1S74, p. 253) "The specimen here described was exhumed by the writer, in June 

 last, from the Pliocene sands of the Niobrara River, Nebraska." (Lull, letter Oct. 23, 1915) "It was collected by the 

 expedition [Yale College] of 1S73, somewhere along the Niobrara River, east of Antelope Creek, Nebraska, by H. Clifford 

 and Professor Marsh." The exact locality has not been determined; it is somewhere within fifty miles of Antelope Creek. 

 Nebraska formation, Upper Miocene. 



Type. — Yale Mus. 13007. (Marsh, 1874, p. 252) "A new genus of solipeds, allied to Equus, is well represented in 

 the Yale Museum by two partial skeletons, with the more important portions preserved, and by numerous fragmentary 

 remains." The main type of P. pemix, Yale Mus. 13007, is of an old individual. (Lull, letter Oct. 23, 1915) "Cata- 

 logue number 13007 and 13007a, mainly one individual but evidently including part of another. The main individual 

 [Yale Mus. 13007] consists of portions of a skull, jaws, the right pes, part of the left tibia?, and so on. Also the left manus, 

 radius, ulna and humerus, and several vertebra?. The left superior premolar series is complete." Measurements: (Marsh, 

 1874) extent of four upper premolars .0S8; three upper molars .068; of lower molar series, po-m 3 , .146; length of radius 

 .253; length of third metatarsal .208. 



Type figure — Plate 28.1, text Figs. 120, 121, 122 of this Memoir. 



Characters. — (Marsh, 1874, p. 252) (1) Differs from Protohippus in the absence of lateral digits, which are only 

 represented by slender splint bones; (2) presence of large antorbital [lachrymal] fossa; (3) presence of functional first 

 upper premolar. (4) First lower premolar wanting; (5) molars with short crowns and distinct fangs; (6) enamel folds of 

 the molar teeth very simple; (7) skull comparatively short; (8) ulna shaft incomplete at centre; (9) distal end of ulna and 

 fibula coalesced with radius and tibia respectively; (10) small trapezium; (11) a rudiment of the fifth metacarpal attached 

 to the unciform; (12) limbs more elongate than in Equus asinus; (13) size about that of Equus asinus; (14) ungual pha- 

 langes broader and slightly cleft at their extremities; (15) relatively large cubo-astragalar facet. (Gidley, 1907, p. 893) 



