248 O. C. Marsh—New Tertiary Mammals. 
species of the genus in the number and general structure of 
the teeth, and in the absence of the posterior intermediate lobe 
of the upper molars, and especially in the presence of the fifth 
digit in the manus. It differs in the much deeper transverse 
ir wi rowns. The 
Measurements. 
Antero-posterior at of penultimate upper molar,..- 9°™ 
Greatest transverse diameter, .----.-...---.--+------. 12 
Extent of lower molar "setien, ee ee curw cscs 48° 
Extent of lower premolar series, - Sh ee 
ebiety Losier or Sense of last lower premolar, - easyer 8°5 
ener Gin 6° 
Depth of jaw ioe ‘third lower Se a gga E eeie 14 
This species occurs in the upper Eocene deposits of Utah. 
Mesohippus, gen. nov. 
This genus presents characters intermediate between Oro- 
hippus* Marsh, and Anchitherium von Meyer. The skull and 
teeth are very Nesine to those of the latter genus, and the den- 
tal formula is the same. In the feet, however, the lateral digits 
are larger; the fifth metacarpal is represented by an elongated 
splint bone; and the second and third cuneiform bones of the 
pes are not coossified. The type of the genus is Mesohippus 
Bairdi, = Anchitherium Bairdi Leidy. Mesohippus celer, = Ancht- 
therium celer Marsh, is a smaller species. Both are from the 
Miocene. 
Thinohyus lentus, gen. et sp. nov. 
This genus is nearly related to Dicotyles, and apparently rep- 
resents an earlier form of the same type. is is shown in the 
similar structure of the skull, and form of the teeth. The most 
boas of the same bulk—and cnek convoluted. There is 4 
Bong. bony tentorial ridge. The molar teeth have the prinei- 
pel ee: more isolated than in Dicotyles, and the intermediate 
obes larg 
In ae sient species the temporal fosse are separated above 
only by a narrow ridge. The auditory bulle are large, and 
oval in outline. The nasal bones are broad posteriorly. The 
*Tn several recent oe Prof. Cope has referred the — Orohippus 
to Hipposyus Leidy. 
e two, rte as shown by a compariso: f the type 
to the praak 
specimens, have no Beet the latte tter belonging Qua 
< aa 
¢ 
Bs 
‘5 
i 
+ 
Ny 
4 
i 
