HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 229 
would be true that associated with them in the case of the female there should 
also be found an increase in the pelvic dimensions and provision for a fuller nutrition 
in the pelvic region. 
An attentive study of the material before us shows that the last two require- 
ments are not met. There are two very well preserved ossa innominata of the 
smaller form in which the relative proportions of the bones show that the pelvis, 
so far as its posterior opening is concerned, was relatively smaller in size than is 
the case in the large specimen (No. 1604) which has been selected for restoration 
as a mounted specimen and identified as M. elatus. This specimen consists of the 
os innominatum used in the restoration of the hind limb of M. petersoni, and num- 
bered 1701 in the Catalog of Vertebrate Fossils in the Carnegie Museum, and 
specimen No. 1705." This indicates that these remains were those of a male 
rather than of a female. Strangely enough there is another specimen of the 
smaller form, consisting of the ossa innominata (No. 1705) in which the dimensions 
do show an enlargement, which might allow this part of the skeleton to be regarded 
as that of a female. 
Furthermore, the vascular system of the pelvis, so far as any opinion can be 
formed in relation to it, from the size of the foramina of the posterior dorsals, 
lumbars, and sacrals, was not more abundantly nourished in the smaller form 
than in the larger, if indeed as well nourished. The foramina giving exit to the 
nerves and entrance to the arteries are proportionately larger in the larger form 
than they are in the smaller. The writer is of the opinion that the pelvic bones 
do not show, except in the one instance cited above, as that of a female pertaining 
to the smaller form, that relative increase in the size in proportion to the other 
parts which would imply that the specimens before him were those of female 
animals. In other words, the best preserved pelvis of the smaller creature which 
we possess is in its dimensions proportionately smaller than in the larger animal, 
but in one specimen belonging to the smaller animal we have remains which would 
indicate that we are dealing with the pelvis of a female of the same form. Further- 
more the very great difference in size, a difference, which it has already been 
pointed out, is as great as that between a large rhinoceros and a tapir, seems to 
be too great to be regarded as a merely sexual character. } 
The second hypothesis is therefore rejected, and the writer adopts the third 
hypothesis, namely, that we are dealing in the case of this material with a species 
represented by more or less complete specimens of the skull, the vertebra, the 
19TIn Science, N. S., Vol. XXVIII, p. 810, the numbers 1700 and 1701 were unfortunately reversed. 
No. 1701 applies to the hind limb and 1700 to the fore limb. 
