6 
IIOKN EXPEDITION-MAMMALIA. 
This belt of country includes the greater part of Queensland and New South 
Wales and a portion of Victoria, the southern part of South Australia and the 
inland part of AVest Australia which borders the central desert from Eucla in the 
east, on the Great Australian Bight, to Shark Bay on the western coast line. 
It is separated from the Euronotian by both positive and negative characters. 
Certain genera, such as Myrmecobius, Choeropus, Peragale, and Antechinomys, 
together with numerous species of other genera, are found in it, but not in the 
Euronotian region, in which, on the other hand, are still more numerous genera 
and species not met with in the inland country. To pass from the coastal district 
over the ranges into the inland parts anywhere along the southern and eastern 
part of the continent is not only to leave behind a rich variety of forms, but to be 
brought into contact with a quite different series, often of genera and, to a very 
large degree, of species of marsupials, birds, reptiles, and fishes. 
There is really in Australia a primary division of marsupials into two groups;— 
(1.) Those which require an environment dependent upon and resulting from 
a constant rainfall of twenty-five inches and upwards yearly, and which inhabit 
the Euronotian region. 
(2.) Those which have become modified so as to be fitted to an environment 
dependent upon and resulting from a rainfall of less than twenty-five inches 
yearly. These practically inhabit the remainder of the continent. 
As a sub-division of these, a certain number of forms may be grouped 
together which can exist under the more rigorous conditions of a climate in which 
the rainfall is under ten inches yearly, and it is these which form the marsupial 
fauna of Central Australia. This central marsupial fauna is essentially an 
immigrant one, of comparatively recent date, and the immigration appears to have 
taken place in the main from the southern and western borders. 
To summarise briefly. In times probably just preceding the Pleistocene there 
was a large and well-watered land area in Central Australia inhabited by a well- 
developed marsupial fauna. Across this central area migration took place in the 
main, and certainly so far as the diprotodonts are concerned, from east to west. 
In this way West Australia acquired its diprotodont fauna. Subsequently the 
central area became transformed into a dry, arid region, in which condition it has 
remained until the present day. 
There must, judging by the presence of such species as Macroptis eugenii in 
Kangaroo Island, have been for some time an extension of land to the south of the 
continent stretching across what is now the Great Australian Bight. 
