1893.] The Titanotherium Beds. 217 
showing a perfect articulation with the trapezoid, may be 
found to be of considerable importance as establishing a closer 
relation of Titanotherium to Diplacodon from the upper 
Eocene than has yet been pointed out, especially if this latter 
form should prove to possess a trapezium, as it is now almost 
certain it did. The trapezium, though present in the earliest 
forms of the Titanotheridz, was quite small and soon disap- 
peared entirely, leaving no vestige of a first digit. Among 
many more or less complete fore feet found in the upper part 
of the Lower, in the Middle, and Upper beds, no trapezium has 
yet been found, while several have been found at the base of the 
beds. : 
It is quite probable that those forms of Titanotheriidw with 
three incisors described by Professor Marsh under the generic 
name of Teleodus will be found to possess a trapezium.’ If 
such should prove to be the case, the genus Teleodus, Marsh can 
then be considered as distinguished from that of Titanotherium, 
Leidy by a definite and constant character, viz., the presence 
of a trapezium. Individuals with three incisors collected by 
the writer have invariably been found at the bottom of the 
beds and the small size of other individuals with three inci- 
sors, discovered by other collectors, indicate that they also 
were taken from the same horizon. There would appear, 
therefore, to be little doubt that the presence of a trapezium 
and three incisors are associated in the same individuals. That 
the latter character was not constant is shown by the presence 
of three incisors on one side and two on the other in the same 
jaw, with no alveole for the missing tooth. 
Variations occur also in the number of sacral vertebra. 
But since these are clearly dependent upon the age of the 
individual they are not considered here. All fully adult speci- 
mens show four sacrals, younger ones only two or three. 
In figure 3 the side view of a skull from the base of the 
‘Titanotherium beds is represented, showing the small round 
horncores and long nasals which are characteristic of skulls 
from this horizon. In figure 2 the side view of a skull from 
the Middle beds is represented, showing horncores and nasals 
of medium length. Figure 1 represents the side view of a 
8m. Jour. Sci, June, 1890, p: 524. 
