INTRODUCTION. 
In few, if in any group of Mammals, is our knowledge of spe- 
cies and genera in such a satisfactory condition as is the case 
with the Marsupials and Monotremes. ‘This is entirely due to 
the labours of Mr. Oldfield Thomas, of the British Museum, 
whose results are published in the ‘‘ Catalogue” so often re- 
ferred to in the course of the following pages. 
Under such circumstances, the task of writing a popular 
monograph of the groups in question has been a comparatively 
easy one ; and the present volume must be regarded as little 
more than an abridgment of Mr. Thomas’s work put into a 
~ more popular guise, with the omission of certain osteological 
and other more technical details. Since the publication of 
his ‘Cataiogue” in 1888, a few new species have been dis- 
covered or described, which are inserted in their proper places 
in this book, by far the most interesting of these being the 
Marsupial Mole, representing a type of the Order previously 
quite unknown. Moreover, since the past history of the 
Marsupials has an important bearing on their present very 
restricted geographical distribution, it has been felt that no 
treatise on the group would be complete without some refer- 
ence to this subject. Accordingly, a section of the work has 
been devoted to the consideration of some of the more gener- 
ally interesting extinct representatives of that Order, while it 
