HIPPARION. 195 



Type figure . — Text Fig. 15S of this Memoir. 



Characters. — (Merriam, 1915, pp. 54-55) "In this form the dentition differs noticeably from that of the typical 

 Hipparion mohavense of the Ricardo Pliocene. The protocone is more strongly flattened transversely, while the enamel 

 pattern of the teeth in general shows fewer deep, smoothly-rounded folds. The plications of the enamel in this form 

 tend to be more distinctly angular, and there are more numerous minute folds. The dimensions differ somewhat from 

 those of the typical //. mohavense. The differences in dimensions and in pattern of the cheek-teeth separating this variety 

 from typical H. mohavense may be due in some part to variation in stage of wear, but the characters seem sufficiently 

 marked to require at least tentative recognition in the classification. It is possible that fuller collections may ultimately 

 show an intergradation between this form and H. mohavense." 



7 



Fig. 158. Hipparion mohavense callodonte Merriam, Univ. Cal. Pal. Coll. 21311, original figures of upper and lower 

 grinding teeth of the type. Natural size. After Merriam. 1915. figs. 5-7, p. 53. 



PLIAUCHENIA PLIOHIPPUS SPECTANS ZONE. 15. EARLY MIDDLE PLIOCENE. 



This zone is typified in the Rattlesnake formation of Oregon. 



Hipparion sinclairi Wortman 1882. 

 Text Fig. 159. 



Hippotherium sinclairi, Wortman, Jacob L. "On the Origin and Development of the Existing Horses," Kansas City Rev. Sci. and 

 Industry, Vol. VI, No. 2, June, 1882, p. 73, no figure. Hippotherium sinclairii, Wortman, Cope, Edw. D. "A Review of the North 

 American Species of Hippotherium." Proc. Amer. Philos. Soc. Vol. XXVI, 1889 (sig. dated June 1, 1889), pp. 434-435, figs. 2, 2a. 



Horizon and locality. — Cottonwood Creek, Oregon, Rattlesnake formation, Upper Miocene. Type collected by 

 J. L. Wortman. 



Type. — (Wortman) Amer. Mus. Cope Coll. 8178, upper premolar of the left side. Measurements: (Gidley, 1907) 

 diameters of crown a.p. .020, tr. .0195, length of crown .042. 

 Type figure. — Text Fig. 159 of this Memoir. 



Characters— (Wortman, 1882, p. 73, Cope, 18S9, p. 435, Gidley, 1907) (Wortman) "H. sinclairi.— Antero- 

 internal lobe slightly concave on its inner border, and elongated fore and aft; much larger than posterior internal lobe." 

 (Cope) (1) Readily distinguishable from the corresponding tooth of H. occidentalc by its inferior size and relatively 

 smaller transverse diameters; dimensions about those of Hippodon speciosus Leidy, differing from that species in the 

 larger and flatter inner column [protocone], long-crowned, and less complex folds of the borders of the lakes; (2) crown 



