PLIOHIPPUS. 



155 



(W. D. M., 1915) The fore limb of the type of Pliohippus pernix indicates that Mtc. Ill thickens slightly toward 

 the distal end, not unlike Troxell's specimen of Pliohippus. The hoof is of a broad, flat type. Mtc. II carries a small 

 facet for the trapezium. 



A referred specimen is Amer. Mus. 10836. 



Pliohippus robustus Marsh 1874. 

 Text Fig. 123. 



Pliohippus robustus, sp. nov., Marsh, 0. C. "Notice of New Equine Mammals from the Tertiary Formation," Amer. Jour. Sci. 

 and Arts, (3) Vol. VII, No. 39, March, 1874, p. 253, no figure. 



Horizon and locality. — (Marsh) " The known remains of this species were found by the writer, last summer [i. e. 

 1873], in the Pliocene strata of the Niobrara River." (Lull, letter of Oct. 23, 1915) "Collected by the expedition of 



Fig. 123. Pliohippus robustus Marsh, Yale Mus. 13008, superior molars of type. (Left upper centre) Crown view 

 of right p 2 ; (left lower) crown view of left p 3 ; (left upper) crown view of right nr. (Two right-hand figures) Outside and 

 anterior views of right nr. All figures natural size. Drawings by S. Oka. 



1S73 from the Niobrara River; collector O. C. Marsh. Type locality probably not far from that of P. pernix" Nebraska, 

 Upper Miocene. 



Type. — Yale Mus. 13008 (Lull, letter Oct. 23, 1915) [A young adult individual] consisting of upper teeth, fragments 

 of the skull, fore and hind feet, radius, humerus, etc. Measurements: (Gidley, 1907) p 2 a. p. .029, tr. .0225; p 3 a. p. 

 .026, tr. .024; m 2 a.p. .025, tr. .022, height of crown, outside, .062. 



Type figure. — Text Fig. 123 of this Memoir. 



Characters. — (Marsh, 1874, p. 253) (1) Of nearly the same size as the type of Pliohippus pernix, but limbs shorter and 

 stouter; (2) the first upper premolar much larger, the upper molars longer and much curved; (3) enamel foldings more 

 complex than in P. pernix, (Gidley, 1907, p. 894) (4) Aside from the difference in the proportions of the bones, the 

 characters assigned by Marsh are indicative of age differences only, the type of P. robustus being a young adult, that of P. 

 pernix an aged individual; (5) the comparative measurements of limb and foot bones indicate that P. robustus is a shorter 



