48 
BULLETIN 57, UNITED STATES NATIONAL MUSEUM. 
Characters . — Dental formula : 
- 2 3. 1. -2 3 4 5 -- .2-2 1-1 3-3 
1 2 -. 1. -2 3 4 5 6 2-2’ ° 1-1 ’ pm 3-3’ 
1-1 
2-2 
=30. 
Teeth without special modifications. Upper incisors in contact 
with each other, but separated from canine by wide diastema, nearly 
terete, their crowns slightly flattened antero-posteriorly, the inner 
tooth of each pair slightly longer than the outer. Lower incisors 
somewhat flattened laterally, the outer of each pair slightly the 
larger; cutting edge blunt, 
nearly flat, though divided by 
a shallow notch into two in- 
conspicuous lobes. Canines 
both above and below with a 
secondary cusp on inner side 
formed by a slight prolonga- 
tion of the cingulum and some- 
what variable in its develop- 
ment in different species. An- 
terior upper premolar perma- 
nent, but scarcely larger than 
incisor in cross section and so 
short as barely to penetrate 
the gum. Its crown is nearly 
flat, though with a faintly in- 
dicated antero-external cusp. 
The corresponding lower tooth 
is considerably larger, its disk- 
shaped crown somewhat con- 
cave except for the minute 
antero - external cusp. The 
three suceeding cheek teeth 
almost exactly resemble each 
other above and below ; pm 3 and ^m 3 are higher and shorter than the 
others, and the inner ridge tends to form a blunt cusp opposite base of 
main cusp ; m 1 , pm 4 , andm t have the longitudinal furrow well de- 
veloped and bounded on the inner side by a distinct, though low, ridge, 
and on the outer side by a much higher ridge, which rises anteriorly into 
a blunt cusp. Their crowns are noticeably longer than broad. The sec- 
ond lower molar closely resembles the anterior lower premolar, except 
that it lacks the small antero-internal cusp. The skull (figs. 5, 6) very 
primitive in form, the ventral profile nearly straight, the dorsal pro- 
file showing no special peculiarities. Floor of brain case scarcely 
