PARAHIPPUS. 



87 



Type. — U. S. Nat. Mus. 5393. Lower jaw fragments containing lower last premolar and first molar of the left side, 

 also last molar from the same specimen as the former. Measurements: (Leidy) space occupied by the back four molars 

 34 lines; space occupied by the back three molars 27 lines; mj a. p. 7-f lines, tr. 7 lines. 



Type figure. — Text Fig. 63 of this Memoir. 



Characters. — (Leidy, 1873) (1) Approaching in size the A. aurelianense; (2) identical in form with Mesohippus (A.) 

 bairdii and A. aurelianense; (3) nearly according in size with Miohippus {A.) condoni. 



is ir 



Fig. 63. Original figures of the lower molar teeth (p4, mi, 1113) of the type of Parahippus agrestis Leidy, U. S. Nat. 

 Mus. 5393. Natural size. After Leidy, 1873, PI. vii, figs. 16, 17. 



TICHOLEPTUS-MERYCHIPPUS ZONE. 9. EARLY MIDDLE MIOCENE. 



This zone is typified by the Mascall of Oregon, and, as described above, is widely distributed in Montana, 

 Colorado, western Nebraska, and Texas, with possible outlyers in California. It is distinguished by 



THE FIRST APPEARANCE OF MeRYC.HIPPUS, SURVIVING P.ARAHIPPUS, KaLOBATIPPUS, AND THE HITHERTO 

 UNRECOGNIZED FORM ArCH&OHIPPUS. 



Parahippus avus Marsh 1874. 



Plates 6.7, 8.6,9,10, 9.4. Text Figs. 64, 65. 



Protoluppus avus, sp. nov., Marsh, O. C. "Notice of New Equine Mammals from the Tertiary Formation," Amer. Jour. Sci. and 

 Ads, (3), Vol. VII, No. 39, Mar., 1874, pp. 253-254, no figure. 



Horizon and locality. — Cottonwood Creek of the John Day River, Oregon, type locality of the Mascall formation, 

 Middle Miocene. Type collected by Thomas Condon. The geologic horizon of this specimen is doubtful; it probably 

 belongs to the Upper John Day rather than to the Mascall. 



Type. — Yale Mus. 11281. (Lull, R. S., letter Oct. 23, 1915.) The type consists of portions of both lower jaws, 

 the right bearing p«-4, mi-2, the left p 2 -4 and mi. There are also nine upper molar and premolar teeth, chiefly of the left 

 side, at least one incisor, and a few tooth fragments. Measurements: (Marsh) space occupied by six upper molars .110, 

 space occupied by three upper premolars, .057, antero-posterior diameter of second upper premolar, .023, transverse 

 diameter, .022, antero-posterior diameter of last upper molar, .017, transverse diameter, .022, extent of three lower pre- 

 molars .0575, antero-posterior diameter of first lower premolar, .0205, transverse diameter, .015, antero-posterior diame- 

 ter of first lower true molar, .018, transverse diameter, .016. 



Type figure.— Plates 8.9,10, text Fig. 61. 



Characters. — (Marsh, p. 251) "The molar teeth have very short crowns, and are inserted by distinct fangs. The 

 enamel is covered with a thick coat of cement. The molars are considerably worn, and the pattern of the enamel thus 

 produced nearly resembles that in the corresponding teeth of Anchitherium, with which the present teeth agree, also, in 

 form and arrangement. . . .The outer concavities of the external lobes are without any median elevation. The posterior 

 inner cone is larger than the one in front. All the lower molars have an outer basal ridge." 



