204 MEMOIRS OF THE CARNEGIE MUSEUM 
These are all interesting questions, and we feel sure that by patient, careful 
study we may approach nearer and nearer the solution. In the inquiry we need 
an imagination broad enough to encompass all the possibilities; but the conclu- 
sions must be based on evidence alone. We must carefully avoid the accumulation 
of a chaos of facts on the one hand, and a glittering but frail structure of theories on 
the other. ‘These problems furnish-an ideal toward which to work. ‘There are data 
bearing on nearly all; yet it is not expected that all can be completely solved here. 
It will require all the data available and all the talent of all the men working in 
this field of investigation to even approximately solve them; yet it is felt by the 
writer that certain aspects of the problems can be better seen by becoming more 
familiar with a certain area the boundaries of which aré more or less definite, and 
where so many different horizons, with their several faunas, are represented. 
The work done by the writer in this region has been primarily that of collect- 
ing, and there has not been time for an accurate survey of the extensive field; yet 
a large number of observations have been made, and many data have been col- 
lected from other sources bearing on the solutions of the problems here involved. 
As the data have accumulated, conceptions apparently more and more in harmony 
with the facts have gradually taken the place of ideas at first entertained. 
It was originally intended to prepare the material and embody it in one compre- 
hensive memoir, but this requires years of work, and it would too long defer the 
publication of interesting discoveries and results.” It has been thought best, there- 
fore, to issue 1t in parts uniform in style, so that if required, the parts can be bound 
together in one complete volume, after all have been issued. 
To Dr. Wm. J. Holland, the Director of the Museum, and, since the death of 
Mr. J. B. Hatcher, the acting Curator of Vertebrate Paleontology, I am indebted 
for the free and unrestricted use of the material. ‘The Montana fossils were col- 
lected by myself, or by expeditions in my charge. ‘The drawings for this issue were 
made by Mr. Sydney Prentice, the draftsman for the Carnegie Museum. 
PART I. A NEW MONOTREME-LIKE MAMMAL. 
Xenotherium unicum gen. and sp. nov. 
(Plate XXIL., Figs. 13, 14, 15 and 16.) 
One of the most interesting specimens from the Titanotherium Beds at Mce- 
Carty’s Mountain is a nearly perfect skull, which is unlike that of any Eutherian 
mammal with which I am acquainted; but in most of its characters is very much 
like the living Monotremes of the Australian region. The only essential skull 
