PYROTHERIUM 165 
character, being oval in cross section and having enamel 
on the front face only. These first incisors are directed 
downward, so that their ends stand between and very 
slightly in front of the second incisors. The end of each. 
is worn bluntly round in contrast to the beveled end of 
inc. 2. The second incisor is larger, rootless, and perma- 
nently growing, with a hollow base, enamel on the front 
face only, and oval in cross section. Both these teeth 
have a layer of cement on them, extending some distance 
beyond the alveolus. The tips are worn in a long bevel 
on the posterior side, very much as is the case on the 
incisors of rodents. 
The third upper incisor, the canine, and premolar 1 
are lacking, a long diastema occupying their place, out 
of which they have been crowded by the development 
of the enormous root of inc. 2, which extends 150 mm. 
and more back into the jaw. P. romeri is distinguished 
from the others by pm. I being present. 
The teeth of the upper premolar-molar series have their 
crowns expanded, and the two series of either side have 
moved toward each other; until in front they are in con- 
tact while in the rear they are only 50 mm. apart, narrowing 
the palate in a unique manner, and giving the impression 
that the palate is mostly a grinding surface. The pre- 
molars are completely molariform and the whole series 
is at an advanced stage of specialization. 
Premolar 2 is three-rooted, with a triangular crown on 
which are three mamma-like tubercles, the larger one in 
front, and two behind. As the crown is worn, these unite 
into a flat, grinding surface, surrounding a central pit 
which opens behind. Premolars 3 and 4 and all the molars 
are large, four-rooted, quadrilateral teeth, each with two 
transverse crests running clear across the crown, and with 
a small cingulum across the anterior margin. Before they 
are worn, the top of each crest is tuberculated, and the 
cingulum is crenulated. In wearing, the anterior face 
