52 The Extinct Rodentia of North America. | January, 
‘and near the orbit. Postorbital processes; no sagittal crest. 
Fic. 6,—Cranium, jaws and 
teeth of Meniscomys Be bal 
Cope, from the John D 
f Oregon; natural Sie aad 
enlarged 
The characters of the dentition of this 
genus resembles those of the genus 
Pteromys, which includes the large fly- 
ing squirrels of Asia and the Malaysian 
archipelago, to which region they are 
confined. The superior molars differ 
from those of Pteromys in wanting all 
re-entrant enamel inflection. 
The general characters of the skeleton 
are unknown. A femur is rather slen- 
der, and a tibia rather elongate, showing 
that the limbs are not short. 
Four species of this genus are known 
to me, all from the John Day Miocene 
of Oregon. They differ considerably in 
the details of the structure of the mo- 
lar teeth. Those of the Meniscomys 
hippodus are more prismatic than those 
of the other species, and the external 
face is not inflected at the grinding sur- 
face as in them. Nevertheless the molars 
have short roots. The arrangement of the crests of the crown of 
Fic. < == pern cavatus 
Caper P of cranium and lo 
‘aw of one e individual from the Joh nitens Marsh, they are complex and 
much wrinkled, whiletperowers molars — 
Day river, ih a nat. size 
enlarged, Origina 
the superior molars is a good deal 
like that to be seen in the molars of 
some of the later three-toed horses, 
if the cementum be removed. (Fig. 
6.) 
In the M. cavatus Cope (Fig. Z% 
the constitution of the superior molars 
is more complex, while that of the — 
inferior molars is more simple. The 
bulla of the ear is set with simple 
transverse septa within, while in the 
M. hippodus their internal face has — 
a reticulate structure like tripe. The — 
superior molars of the M. Holophus . 
Cope (Fig. 8, a, 6) have their crests — 
ower and cusps unwrinkled. In. the 
e 
