The species of the genera Petrogale and Bettongia are common to New South Wales, South Australia, and the North-west Coast; but they are not found in Van Diemen’s Land, and the genus Myrmecobius appears to be peculiar to Western Australia, for it is not by any means certain that the red shrew-mouse discovered in Australia Felix by Sir T. Mitchell belongs to this genus.

The Genera Thylacinus, Diabolus, and Dromicia, are peculiar to Van Diemen’s Land.

The species of the genera Dasyurus and Perameles are very abundant in Van Diemen’s Land, but they have also representatives which are found in New Holland.

The species of the genera Nyctophilus, Phalangista, Hepoona, Phascogale, Macropus, Halmaturus, Hypsiprymnus, and Hydromys, appear to be common to all parts of the continent, and also to Van Diemen’s Land.

The genera Echidna and Ornithorhynchus are found in New Holland and Van Diemen’s Land, but I have not heard of their having been discovered in the Western or Southern parts of the continent of Australia.

There are some of the genera of the non-Marsupial animals, as Rhinolophus and Pteropus, which are common to various parts of Australia and the different parts of the Old World, and others, as Canis, Mus, Scotophilus, and Molossus, which are common to it and to both Hemispheres.  Two Marsupial genera, Halmaturus and Perameles, have species found in New Guinea, but most probably, when they have been more carefully examined, they will be found to form a peculiar genus, allied to the Australian animals, as is the case with the tree-kangaroos (Dendrolegus) and the Phalangers (Cuscus) of that country.  We have a specimen of the Halmaturus in the British Museum, from the Leyden collection, but like many of the specimens in that collection, where the zoological specimens are made subservient to the anatomical predilections of the conservator, it has no skull, and false claws, which renders it impossible for me to define its characters.  The tail has rings of scales under the hair, but this is also the case with most Halmaturi.

Before proceeding to the consideration of the distribution of the species, over the different districts of Australasia, it may be remarked that this is a subject surrounded with considerable difficulty, as different naturalists do not always apply the same test to determine the distinction of the species, some considering the differences found in the specimens from different localities, as merely local varieties, and others regarding them as distinct; and others again declaring that several specimens, which cabinet naturalists are in the habit of regarding as only accidental varieties from the examination of the skins, are quite distinct when they are observed alive in their native habitat.  In the preceding list, when all the specimens I have seen from a particular habitat have a similar and peculiar character, I have considered them as species; on the contrary when the specimens from the same locality offer variations among themselves, as in those of the genus Hepoona, where the extent of the whiteness on the tail, and the variation in the colour of the body appear to differ in the specimens from the same place, I have regarded them as belonging to the same species, believing it to be a variable species which has an extensive range.