[903.] Gidley, A New Three-Toed Horse. 467 



Neohipparion whitneyi, gen. et sp. nov. 



Generic characiers. — Protocone free, except at l^ase, as in Ilip- 

 parioii. Protocone comparatively large and mucli exjjanded antero- 

 posteriorly. Enamel foldings sim])le. The median external basal 

 column present in the lower milk molars as in Hipparion, Init niucli 

 shorter and more expanded antero]josteriorly. Lateral digits much 

 reduced. 



Specific characters. — Size about ecjual to Neohipparion occideiitalc, but 

 enamel foldings much more simple, even more sim])le tlian in .V. affine. 

 N. lehitneyi further differs from .V. affine in the much stronger develop- 

 nn-nt of the styles of the ectolojili. Protocone relatively large and 

 very much elongated in cross-section anteroposteriorl3^ Outer wall 

 of th-e protocone flat and slightly folded inward, as is usual in Equus 

 caballns. Metapodials very long and slender. Lateral digits greatly 

 reduced, their terminal phalanges not extending to the distal end of 

 the first phalanx of the median digit. 



Although the collected material representing the Miocene 

 horses of America is very abundant, it is, for the most part, 

 so fragmentary and the different parts of the skeleton so un- 

 certainly associated that most of the species are known only 

 from the teeth. Hence the present specimen, though not in 

 the line of ancestry of any of the living horses, may serve as 

 a standard for comparison of equal value with Mcsohippus 

 bairdii, so fully described by Scott,' and may be described in 

 detail as follows : 



I. The Dentition. 



Dental formula I.f, C.|, P.^, M.'|. In jjroportion to the 

 other parts of the skeleton the teeth arc very large compared 

 with those of Equus cahallus. The molars and ])remolars of 

 both jaws are heavily cemented. 



The Upper Jaw. — The tooth-crowns, though strongly hyp- 

 sodont, are of moderate length. Incisors much shorter than 

 in Equus. P' is placed well back, extending but little for- 

 ward of the anterior lobe of p" to which it is closely appressed 

 on the inner side. This position brings it in opposition with 

 the anterior lobe of pa of the lower jaw. 



The external styles of the molars and premolars are as 



journal of Morphology, Vol. V. i.Syi, pp. 301-342. 



