1. Species of _Rajidæ_ (_Raja_, _Trygon_) prefer the mouths of rivers, probably because the muddy or sandy bottom offers the most suitable conditions for fishes which can feed on the bottom only; such brackish water species belong chiefly to the Equatorial Zone, some having taken up their abode entirely in fresh water (South American Trygons). 2. _Ambassis_, a Percoid genus, consisting of numerous small species, inhabiting the shores of the tropical parts of the Indian Ocean and the coasts of Tropical Australia. Many species enter, and all seek the neighbourhood of, fresh water; hence they disappear in the islands of the Pacific, and are scarce in the Red Sea. 3. _Therapon_, with the same distribution as the former. 4. Numerous _Sciænidæ_ of the Equatorial Zone. 5. The _Polynemidæ_, chiefly inhabitants of brackish water of the Equatorial Zone, most developed in the Indian region, and scarce in the Tropical Pacific. 6. Numerous species of _Caranx_ (or Horse Mackerels) of the Equatorial Zone. 7. Nearly all species of _Gastrosteus_ enter brackish water, _G. spinachia_ being almost exclusively confined to it: Northern Zone. 8. The most important genera of the Gobies (_Gobiina_): _Gobius_ (nearly cosmopolitan), _Sicydium_, _Boleophthalmus_, _Periophthalmus_, _Eleotris_ (equatorial). Many of the species are entirely confined to fresh water. 9. The _Amblyopina_, similar to the Gobies, but with more elongated body: Tropical Indo-Pacific. 10. The _Trypauchenina_: Coasts of the Indian region. 11. Many species of _Blennius_, of which several are found far inland in fresh waters--for instance in North Italy, in the Lake of Galilee, in the eastern parts of Asia Minor. 12. The majority of _Atherinidæ_, and 13. The _Mugilidæ_: both families being most numerous and abundant in brackish water, and almost cosmopolitan. 14. Many _Pleuronectidæ_ prefer the mouths of rivers for the same reason as the Rays; some ascend rivers, as the Flounder, _Cynoglossus_, etc. 15. Several _Siluridæ_, as especially the genera _Plotosus_, _Cnidoglanis_, _Arius_, which attain their greatest development in brackish water. 16. The _Cyprinodontidæ_ are frequently found in brackish water. 17. Species of _Clupea_, some of which ascend rivers, and become acclimatized in fresh water, as _Clupea finta_, which has established itself in the lakes of northern Italy. 18. _Chatoessus_, a genus of Clupeoid fishes of the Equatorial Zone, of which some species have spread into the Northern Zone. 19. _Megalops_: Equatorial Zone.