494 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 92 
Order PERISSODACTYLA 
NANNIPPUS cf. PHLEGON (Hay) 
FIGurE 40 
The type of Nannippus phlegon, an isolated lower cheek tooth from 
the Blanco of Texas, was originally described by Cope’ as Equus 
minutus, ® Name preoccupied by Hguus minutus Marcelles de Serres 
and probably by #. minutus Dubois. Because of this Hay * proposed 
the name L'quus phlegon for the minute Blanco horse, and subsequently 
this species has been referred to most of the later Tertiary equid genera, 
including Merychippus by Hay, Protohippus by Gidley, Pliohippus 
by Osborn, and Hipparion by Matthew, until 
Matthew ** in 1926 proposed the subgeneric name 
Nannippus, under Hipparion, for its reception. 
Nannippus has since come to be regarded as of 
generic rank, 
The published record of the culminating stage 
of this specialized HWipparion-like horse is 
rather scant although it is known to be repre- 
sented in several late Pliocene deposits in the 
Southwest. Matthew’s characterization, rather 
brief and based on material from the Blanco 
beds, 1s as follows: 
One group of small American species (new subgenus 
Nannippus) has the teeth very long crowned, up to a 
fourth longer than in any living horse; oval protocones 
and extremely slender limbs and feet, in which the side 
toes are complete but no trace remains of the fifth digit 
and trapezium. This group is typified by Hipparion 
phlegon of the Blanco formation, of which I secured 
skulls, feet, ete., in 1924. Contrast it with the contempo- 
rary Plesippus, with stout limb and foot bones, the side 
toes reduced to splints but the trapezium and fifth digit 
still retained. 
Figure 40.—Nannippus ih) RE alae iat cilile i 
Enis Three incomplete lower jaws with milk denti- 
Right ae cheek tions, several isolated teeth, foot bones, and frag- 
tooth (U.S.N.M. No. Sig ae SOUS) iT a i 
ies otecie es eos of limb bones from the Benson locality 
and occlusal views. belong to a small Hipparion-like horse, which 
x1. Benson upper Hi: : y : 
: 1 ae ' + * ; - = 
plieecuen AHee ad seems with little doubt to represent Nannippus 
phlegon, although the material from the Blanco, 
which Matthew collected, was never illustrated or adequately de- 
scribed. The Benson Vannippus has extremely hypsodont cheek teeth 
of rather small cross section, and these may show noticeable curva- 
0K. D. Cope, 4th Ann. Rept. Geol. Surv. Texas, for 1892, pp. 67-68, 1893. 
10, P. Hay, Amer. Geol., vol. 24, p. 345, 1899. 
uz W. D. Matthew, Quart. Rev. Biol., vol. 1, p. 165, 1926. 
