But at the time when this narrowing of the sea took place in one direction, there must have been a greater separation at the other end of the chain, or we should find more equality in the numbers of identical and representative species derived from each extremity. It is true that the widening of the strait at the Australian end by subsidence, would, by putting a stop to immigration and intercrossing of individuals from the mother country, have allowed full scope to the causes which have led to the modification of the species; while the continued stream of immigrants from Java, would, by continual intercrossing, check such modification. This view will not, however, explain all the facts; for the character of the fauna of the Timorese group is indicated as well by the forms which are absent from it as by those which it contains, and is by this kind of evidence shown to be much more Australian than Indian. No less than twenty-nine genera, all more or less abundant in Java, and most of which range over a wide area, are altogether absent; while of the equally diffused Australian genera only about fourteen are wanting. This would clearly indicate that there has been, until recently, a wide separation from Java; and the fact that the islands of Bali and Lombock are small, and are almost wholly volcanic, and contain a smaller number of modified forms than the other islands, would point them out as of comparatively recent origin. A wide arm of the sea probably occupied their place at the time when Timor was in the closest proximity to Australia; and as the subterranean fires were slowly piling up the now fertile islands of Bali and Lombock, the northern shores of Australia would be sinking beneath the ocean. Some such changes as have been here indicated, enable us to understand how it happens, that though the birds of this group are on the whole almost as much Indian as Australian, yet the species which are peculiar to the group are mostly Australian in character; and also why such a large number of common Indian forms which extend through Java to Bali, should not have transmitted a single representative to the island further east.
The Mammalia of Timor as well as those of the other islands of the group are exceedingly scanty, with the exception of bats. These last are tolerably abundant, and no doubt many more remain to be discovered.
Out of fifteen species known from Timor, nine are found also in Java, or the islands west of it; three are Moluccan species, most of which are also found in Australia, and the rest are peculiar to Timor.
The land mammals are only seven in number, as follows: 1. The common monkey, Macacus cynomolgus, which is found in all the Indo-Malayan islands, and has spread from Java through Bali and Lombock to Timor.
This species is very frequent on the banks of rivers, and may have been conveyed from island to island on trees carried down by hoods. 2.
Paradoxurus fasciatus; a civet cat, very common over a large part of the Archipelago. 3. Felis megalotis; a tiger cat, said to be peculiar to Timor, where it exists only in the interior, and is very rare. Its nearest allies are in Java. 4. Cervus timoriensis; a deer, closely allied to the Javan and Moluccan species, if distinct. 5. A wild pig, Sus timoriensis; perhaps the same as some of the Moluccan species. 6.
A shrew mouse, Sorex tenuis; supposed to be peculiar to Timor. 7. An Eastern opossum, Cuscus orientalis; found also in the Moluccas, if not a distinct species.