In South-western Australia a mingling of the scanty fauna with that of the southern temperate parts takes place. _Oligorus macquariensis_ (The Murray Cod), which has a congener on the coast of New Zealand, ascends high up the Murray river, so that we cannot decide whether this Percoid should be located in the Tropical or Temperate part of Australia. Several _Galaxias_ also extend to the confines of Queensland, and will probably some day be found members of this region. In the smaller Pacific islands the Freshwater fishes exhibit a remarkable sameness: two or three species of _Dules_, several Eels, an Atherine, or some Gobies, Mullets, and other fishes which with equal readiness exchange fresh for salt water, and which would at once reach and occupy any streams or freshwater lakes that may be formed on an island. The Sandwich Islands are the only group among the smaller islands which are tenanted by a Siluroid, a species of _Arius_, which is closely allied to Central American species, and, therefore, probably immigrated from Tropical America. II. NORTHERN ZONE. The boundaries of the Northern Zone coincide in the main with the northern limit of the Equatorial Zone; but at three different points they overlap the latter, as has been already indicated. This happens in, and east of, Syria, where the mixed faunæ of the Jordan and the rivers of Mesopotamia demand the inclusion of this territory into the Northern Zone as well as the Equatorial; in the island of Formosa, where a Salmonoid and several Japanese Cyprinoids flourish; and in Central America, where a _Lepidosteus_, a Cyprinoid (_Sclerognathus meridionalis_), and an Amiurus (_A. meridionalis_) represent the North American fauna in the midst of a host of tropical forms. A separate _Arctic_ Zone does not exist for Freshwater fishes; ichthyic life becomes extinct towards the pole as soon as the fresh water remains frozen throughout the year, or thaws for a few weeks only; and the few fishes which extend into high latitudes, in which lakes are open for two or three months in the year, belong to types in no wise differing from those of the more temperate south. The highest latitude at which fishes have been obtained is 82° lat. N., whence the late Arctic Expedition brought back specimens of Charr (_Salmo arcturus_ and _Salmo naresii_). The ichthyological features of this zone are well marked: the Chondrosteous Ganoids or Sturgeons, and the families of _Salmonidæ_ and _Esocidæ_ are limited to, and characteristic of, it; Cyprinoids flourish with the Salmonoids, both families preponderating in numbers over the others, whilst the Siluroids are few in number and in variety.