No. 397-] ZOOLOGY OF THE HORN EXPEDITION. 29 
dide, Rana, Heteronota, Physignathus, Pericheta, and from 
the Austro-Malayan area, and later, for the passage northward 
of monotremes and marsupials. The union with New Zealand 
was severed, and only that with New Guinea probably remained 
at the time when the Prototheria and Metatheria had become 
established on the Australian continent. 
4. Perhaps in later Cretaceous times, and certainly not later 
than the Miocene, a union with South America by way of Tas- 
mania and Antarctica resulted in the introduction of such forms 
as Gundlachia, Geotria, Galaxias, Haplochiton, Aphritis, and the 
Cystignathidee, Marsupialia, and possibly the Monotremata. 
5. The union of eastern and western Australia, and the for- 
mation during the Tertiary period of a great lacustrian area and 
of pluvial conditions in the interior, favored the development of 
the gigantic diprotodont and struthious forms of the Pliocene 
period. ; 
6. The elevation of the coastal range barrier, which was much 
higher in Tertiary times than at present, prevented the free inter- 
mingling of the coastal forms with those of the inland regions. 
7. The isolation of the Australian continent, by the oblitera- 
tion of the land connections referred to, has preserved to a great 
extent its unique animal life. The union with Tasmania was 
doubtless severed prior to the Pliocene times, when the dingo 
and large diprotodonts existed in Australia. 
8. The desiccation of the interior in Post-Pliocene times partly 
replaced and partly intensified the mountainous barrier near the 
coast, and combined with this to separate the desert fauna from 
that of the well-watered districts. 
After careful study of the animals collected.by the Horn 
Expedition, and comparison with specimens from the remainder 
of the continent, Professor Spencer concludes that western 
Australia has no claim to the title ** Autochthonian," as far as the 
higher forms at least are concerned. He discards this term, 
which was introduced by Professor Tate with reference to the 
flora. The Euronotian region of the same author he finds made 
up of two well-defined areas, each of which is marked by charac- 
teristic animal forms, and prefers to divide the Australian region 
as follows : 
