28 THE AMERICAN NATURALIST. [Vor. XXXIV. 
of western Australia, and that the monotremes and polyproto- 
donts diminish in importance as we pass northward and north- 
westward from southeastern Australia. 
The birds collected range over the southern portion of the 
continent from east to west, with a slight preponderance of 
western forms. The reptiles show a marked affinity with the 
west and north. The Amphibia, with the exception of Hyla ru- 
bella, are allied to those of the southeastern portion. The fishes 
are related to those of the coastal districts, and not to those of 
the Murray River system ; they probably were derived from 
the north. The mollusks are related to the west, and, in a 
slight degree, to the eastern interior. The other invertebrates 
in the center are too imperfectly known to furnish reliable 
generalizations. 
As a result of his investigations, Professor Spencer draws 
some highly interesting conclusions in respect to the faunal 
affinities of the island continent and the geologic changes that 
have combined to establish this remarkable life here. These 
views, while they differ in some marked particulars from those 
of Darwin, Wallace, and Lydekker, are, we believe, in line with 
the very latest scientific developments. They may be stated 
briefly as follows : 
1. Probably a very ancient connection with southeastern 
Asia, existing partly in the western and partly in the eastern 
portions of the island, when these were separate land masses, 
furnished the original inhabitants, which are represented to-day, 
perhaps, by such forms as Xanthomelon, Peripatus, Ceratodus, 
Amphibolurus, Moloch, and the families Pygopodide, Melipha- 
gide, and Trichoglossida. 
2. A great marine area, in which the Upper Cretaceous rocks 
of the Rolling Downs were deposited, completely separated 
the western and eastern portions and isolated the higher Steppes 
from the ancient region further west. 
3. Across the Torres Straits a connection in late Cretaceous 
times with a Papuan area, and with Polynesia and the New 
. Zealand region, accounts for the distribution of Microphyura, 
Acanthodrilus, and the struthious birds of Australia and New 
Zealand ; also for the introduction of the Paradiseide, Megapo- 
