162 



osborn: OLIGOCENE, MIOCENE, pliocene eqtjime. 



Pliohippus leidyanus sp. nov. 



Plates 2S.3, 29, 30.1,2. Text Fig. 129. 



Horizon and locality. — From the Snake Creek formation, Sioux County, western Nebraska. Type collected by Harold 

 J. Cook for the American Museum of Natural History in 1915-1916. 



Type. — Amer. Mus. 17724. Skull, jaws, vertebrae, fore and hind limbs, considerable portions of the ribs and other 

 parts of the skeleton, all of one individual. The dentition indicates that the type is a nearly adult female, about six years 

 of age, the last grinding tooth, m 3 , just coming into use. 



Type figure — Plates 29, 30, text Fig. 129 of this Memoir. 



Characters. — (1) Intermediate in size between the Niobrara species Pliohippus supremus, P. robustus, P. pcrnix and 

 the Republican river species P. nobilis, (2) Orbits small; (3) malar and lachrymal fossa? absent; (4) shallow maxillary 

 fossae just anterior to the junction of the maxillaries with the lachrymals (Plate 30.1). (5) Grinding teeth similar in enamel 

 pattern to other species of Pliohippus in similar stages of wear, i. e. plications relatively simple; (6) grinding teeth (Plate 



30.2) more elongate than in P. supremus (Fig. 118) and P. robustus (Fig. 123). 



The type skull and dentition appear to be specifically distinct from previously described 

 forms in the exceptional position of the preorbital fossa? on the sides of the maxillaries, as con- 

 trasted with the very distinct double, or lachry mo-malar fossae in the types of P. mirabilis, P. 



♦ 



supremus, P. pcrnix, P. lullianus, and P. nobilis. 



Facial pits. — Comparison of these fossa; in male and female skulls of Mcrychippus, 

 Protohippus, and Pliohippus, as represented in Plates 20-30 of this Memoir, indicates that they 

 are secondary sexual characters, strong and double in males, single and feebly developed in 

 females. The closest analogy to the maxillary fossa? of the P. leidyanus female type is another 

 female type, namely, Protohippus niobrarensis Gidley (Plate 21.2), also the female neotype of 

 Protohippus perditus (Plate 21.3). 



The finely preserved fore and hind feet confirm the evidence afforded in the type of P- 

 lullianus that these animals are absolutely monodactyl, or solipedal. 



Pliohippus tantalus Merriam 1913. 

 Text Fig. 130. 



Pliohippus (?) tantalus, n. sp., Merriam, John C. "New Protohippine Horses from Tertiary Beds 

 on the Western Border of the Mohave Desert," Univ. Cal. Publ. Bull. Dept. Geol. Vol. 7, No. 23, Dec. 22, 

 1913, pp. 440-441, figs. 4a, 4b. 



4b 



Fig. 130. Original 

 figures of the type of 

 Pliohippus tantalus 

 Merriam, Univ. Cal. 

 Pal. Coll. 19434, p 4 

 (?). Natural size. 

 After Merriam, 

 1913, figs. 4a, 41>, 

 p. 441. 



Horizon and locality. — From the Ricardo formation, Lower Pliocene, El Paso range, South- 

 ern California. Type collected by expedition of the University of California. 



Type— (Type) Univ. Cal. Pal. Coll. 19434 (cotype) 21221. Two large upper cheek teeth. 

 Measurements: (type, 19434), p 4 , a.p. .0248, tr. .024, height of crown .048. 

 Type figure — Text Fig. 130 of this Memoir. 



Characters. — (Merriam, 1913, p. 440) (1) Protocone and protoconule united; (2) crown 

 curved; (3) fossettes large, wide, with complicated enamel on both borders of the metaloph, and with single pro- 

 jections into pre- and post-fossettes; (4) a single crochet fold in the prefossette; (5) a pli caballin; (6) outer styles 

 heavy and narrow, noticeably above the base. 



