276 THE OSTEOLOGY OF ELOTHERIUM. 
same explanation applies to the curious notches sometimes worn in the external upper 
incisor. ‘The numerous specimens examined do not indicate that there was any difference 
between the males and the females in the size of the canines, the tusks being invariably 
large and powerful. If, as here suggested, the canines served other purposes than those 
of weapons, the lack of any such sexual difference would be intelligible enough. 
The premolars are very simple and quite like those of the upper series in shape; 
their crowns are massive, compressed cones, without additional cusps. The cingulum is 
usually prominent, but varies in the different species. P is much the highest of the 
series, especially in #. imperator, where it rises to the full height of the canine, and gives 
a very characteristic appearance to the lower dentition. Pz has its posterior face flat- 
tened, forming an incipient fossa with a number of small tubercles in it. P sand ; stand 
quite close together, and p ; is separated by a short space from the canine, while p; is 
isolated by considerable diastemata both in front of and behind it. 
The lower molars are small in proportion to the size of the jaw and to the space 
occupied by the premolar series. In size they increase posteriorly, and they have a 
simple, quadritubercular pattern, the crowns surrounded by a strong cingulum. There 
is much variation in the development of the fifth or posterior unpaired cusp (hypoconu- 
lid); it is frequently absent and represented only by a strong cingulum, though some- 
times it is present as a distinct cusp on m > or mz. It is less commonly found on m 3 
and only in the very large /. leidyanum is it well developed. 
The Milk Dentition—The temporary canines and incisors differ from the permanent 
ones only in size. It is uncertain whether the first premolar, in either jaw, has a prede- 
cessor in the deciduous series, none of the specimens distinctly showing such a predecessor. 
In one individual, howeyer, the tip of p 1 is just visible in the centre of a large alveolus, 
from which a milk-tooth has apparently been shed. If this change does actually occur, it 
must take place at an early stage, and, on the whole, it seems probable that, at least in the 
upper jaw, the number of deciduous premolars is four. Dp 2 has a compressed, elongate, 
conical crown, without accessory cusps of any kind; it is carried on two widely separated 
fangs, and is isolated by diastemata both in front of and behind it. Dp 2 consists of 
three principal cusps. The antero-external cusp (protocone) is an acutely pointed pyra- 
mid, while the postero-external cusp (tritocone) is lower and smaller. The internal cusp 
(tetartocone) is posterior in position and placed on the same transverse line as the trito- 
cone, while between the two is a small conule. The cingulum is distinct on the front and 
hind faces, obscure on the outer and absent from the inner face of the crown. Dp ¢ is 
molariform, but differs somewhat from the molar pattern in the fact that the postero- 
internal cusp is even more distinctly an elevation of the cingulum and that the posterior 
conule is double. 
