the south their progress was still slower, Tasmania, New Zealand, and Patagonia being without representatives, whilst the streams of the Andes of Chili are inhabited by a few dwarfed forms identical with such as are characteristic of similar localities in the more northern and warmer parts of the South American continent. After these preliminary remarks we propose the following division of the fauna of Freshwater fishes:-- I. THE NORTHERN ZONE.--Characterised by Acipenseridæ. Few Siluridæ. Numerous Cyprinidæ. Salmonidæ, Esocidæ. 1. _Europo-Asiatic or Palæarctic Region_.--Characterised by absence of osseous Ganoidei; Cobitidæ and Barbus numerous. 2. _North American Region_.--Characterised by osseous Ganoidei, Amiurina, and Catostomina; but no Cobitidæ or Barbus. II. THE EQUATORIAL ZONE.--Characterised by the development of Siluridæ. A. _Cyprinoid Division_.--Characterised by presence of Cyprinidæ and Labyrinthici. 1. _Indian Region_.--Characterised by [absence of Dipnoi[18]] Ophiocephalidæ, Mastacembelidæ. Cobitidæ numerous. 2. _African Region_.--Characterised by presence of Dipnoi and Polypteridæ. Chromides and Characinidæ numerous. Mormyridæ. Cobitidæ absent. B. _Acyprinoid Division_.--Characterised by absence of Cyprinidæ and Labyrinthici. 1. _Tropical American Region_.--Characterised by presence of Dipnoi. Chromides and Characinidæ numerous. Gymnotidæ. 2. _Tropical Pacific Region_.--Characterised by presence of Dipnoi. Chromides and Characinidæ absent. III. THE SOUTHERN ZONE.--Characterised by absence of Cyprinidæ, and scarcity of Siluridæ. Haplochitonidæ and Galaxiidæ represent the Salmonoids and Esoces of the Northern zone. One region only. 1. _Antarctic Region_.--Characterised by the small number of species; the fishes of-- _a_. The Tasmanian sub-region; _b_. The New Zealand sub-region; _c_. The Patagonian sub-region; being almost identical.[19] In the following detailed account we begin with a description of the equatorial zone, this being the one from which the two principal families of freshwater fishes seem to have spread. I. EQUATORIAL ZONE.