216 ? The American Naturalist. [March, 
cone. Individuals from the base of the beds show scarcely 
any indications of this cone, but as we proceed upward in the 
beds, there is a marked increase in the development of the inner 
basal ridge on the inner posterior angle of the last upper true 
molar. This development frequently succeeds near the middle 
of the beds in producing a perfect posterior inner cone. 
Other variations are noticeable in the dentition and in the 
character of the nasals, but they are common to individuals 
from any horizon whatsoever, and are thought to be of sexual 
importance only. Among variations of this nature may be — 
mentioned the following: Differences in the size of the canines — 
as compared with the molars and premolars; presence, absence, 
or want of continuity of an inner basal ridge on the superior 
premolars; comparative strength and rugosity of the nasals. 
Since slender and delicate nasals, small canines and upper 
premolars with only a very slight or no basal ridge on the 
inner border, are associated in the same skulls; these skulls 
are considered to have belonged to females, while those skulls 
in the same horizons, with stronger and more rugose nasals, 
larger canines and a well developed inner basal ridge on the 
upper premolars represent their male companions. 
There were also changes taking place in other portions of 
the skeletons of these animals, important among which may 
be mentioned the development of a third trochanter. Femora 
from the bottom of the beds were quite small and with only a 
rudimentary third trochanter. Toward the middle of the beds 
they increase in size and show a well marked third trochanter, 
while at the top of the beds this process has become quite well 
developed and is of moderate size. : 
The most important change that took place in the Titano- 
theriide, and the only one perhaps of generic importance, 8” 
be found in the fore foot. Early in the season of 1886 the 
writer discovered near the base of the Titanotherium beds a 
portion of the skeleton of a very small individual with both 
fore feet and limbs in position. The carpus of this individual 
was found to possess an additional bone (the trapezium) hitherto 
uhknown in the Titanotheriide. This fortunate discovery 
a skeleton, at the base of the deposits, with a distinct trapezium 
