188 



OSBORN: OLIGOCENE, MIOCENE, PLIOCENE EQUIDjE. 



Type figure. — Text Fig. 150 of this Memoir. 



Characters. — (1) Resembling Hipparion affine Leidy in its large size and in the strong lateral compression of the 

 protocone; (2) pre- and postfossettes narrow transversely; (3) enamel showing comparatively few plications; (4) H. 

 gidleyi distinguished from H. affine by its narrow fossettes, wider protocone, and slightly larger size. 



Merriam observes that H. affine and H. gidleyi are evidently closely related and seem to represent nearly the same 

 stage of evolution. 



Hipparion platystyle Merriam 1915. 

 Text Fig. 151. 



Neohipparion, sp., Merriam, John C. "Vertebrate Fauna of the Orindan and Siestan Beds in Middle California," Univ. Cal. Publ. 

 Bull. Dept. Geol., Vol. 7, No. 19, Sept. 24, 1913, pp. 375-376, figs, la, lb, lc. Hipparion platystyle, n. sp. "New Species of the Hipparion 

 Group from the Pacific Coast and Great Basin Provinces of North America," Univ. Cal. Publ. Bull. Dept. Geol., Vol. 9, No. 1, June 29, 

 1915, p._5. 



Horizon, and locality. — (Merriam, 1913, p. 375.) " . . .discovered. . .in extensive Orindan exposures about two and 

 one-half miles from the mouth of Tassajara Canon, on the southwest side of Mount Diablo." California. Lower Pliocene. 

 Type collected by Mr. Williams. 



Type. — Univ. Cal. Pal. Coll. 19830. A second upper premolar, p 2 , of the right side, with the walls of the crown par- 

 tially fractured. Measurements: p 2 a.p. .0258, tr. .0216; protocone a. p. .0082. 



Type figure. — Text Fig. 151 of this Memoir. 



Characters. — (Merriam, 1915, p. 5) (1) Crown large and well cemented; (2) form of the fossettes indicates that the 

 crown was never greatly elongated; (3) protocone pillar small, distinct from the forked pli caballin, and somewhat flat- 

 tened laterally; (4) fossettes narrower transversely than in H. mohavcnse; (5) enamel walls of fossettes plicate, para- 

 and mesostyles heavy; (6) differing from H. mohavensc in its more flattened protocone and narrower fossettes; (7) more 

 nearly resembling the Hipparion forms of the Ricardo, especially in the specimen Univ. Cal. Pal. Coll. 19478. 



