In analysing this list we find that out of 39 families or groups of freshwater fishes 12 are represented in this region, and that 625 species are known to occur in it; a number equal to two-sevenths of the entire number of freshwater fishes known. This large proportion is principally due to the development of numerous local forms of Siluroids and Cyprinoids, of which the former show a contingent of about 200, and the latter of about 330 species. The combined development of those two families, and their undue preponderance over the other freshwater types, is therefore the principal characteristic of the Indian region. The second important character of its fauna is the apparently total absence of Ganoid and Cyclostomous fishes. Every other region has representatives of either Ganoids or Cyclostomes, some of both. However, attention has been directed to the remarkable coincidence of the geographical distribution of the _Sirenidæ_ and _Osteoglossidæ_, and as the latter family is represented in Sumatra and Borneo, it may be reasonably expected that a Dipnoous form will be found to accompany it. The distribution of the _Sirenidæ_ and _Osteoglossidæ_ is as follows:-- _Tropical America._ Lepidosiren paradoxa. | Osteoglossum bicirrhosum. | Arapaima gigas. _Tropical Australia._ Ceratodus forsteri. | Osteoglossum leichardti. Ceratodus miolepis. _East Indian Archipelago._ ? | Osteoglossum formosum. _Tropical Africa._ Protopterus annectens. | Heterotis niloticus. Not only are the corresponding species found within the same region, but also in the same river systems; and although such a connection may and must be partly due to a similarity of habit, yet the identity of this singular distribution is so striking that it can only be accounted for by assuming that the _Osteoglossidæ_ are one of the earliest Teleosteous types which have been contemporaries of and have accompanied the present Dipnoi since or even before the beginning of the tertiary epoch. Of the _autochthont_ freshwater fishes of the Indian region, some are still limited to it, viz., the _Nandina_, the _Luciocephalidæ_ (of which one species only exists in the Archipelago), of Siluroids the _Chacina_ and _Bagariina_, of Cyprinoids the _Semiplotina_ and _Homalopterina_; others very nearly so, like the _Labyrinthici_, _Ophiocephalidæ_, _Mastacembelidæ_, of Siluroids the _Silurina_, of Cyprinoids the _Rasborina_ and _Danionina_, and _Symbranchidæ_. The regions with which the Indian has least similarity are the North American and Antarctic, as they are the most distant. Its affinity to the other regions is of a very different degree:--