3. A closer affinity between the Indian and Tropical American regions than is indicated by the character of the equatorial zone generally, does not exist. No genus of Freshwater fishes occurs in India and South America without being found in the intermediate African region, with two exceptions. Four small Indian Siluroids (_Sisor_, _Erethistes_, _Pseudecheneis_, and _Exostoma_) have been referred to the South American _Hypostomatina_; but it remains to be seen whether this combination is based upon a sufficient agreement of their internal structure, or whether it is not rather artificial. On the other hand, the occurrence and wide distribution in tropical America of a fish of the Indian family Symbranchidæ (_Symbranchus marmoratus_), which is not only congeneric with, but also most closely allied to, the Indian _Symbranchus bengalensis_, offers one of those extraordinary anomalies in the distribution of animals of which no satisfactory explanation can be given at present. 4. The relation of the Indian region to the Tropical Pacific region consists only in its having contributed a few species to the poor fauna of the latter. This immigration must have taken place within a recent period, because some species now inhabit fresh waters of tropical Australia and the South Sea Islands without having in any way changed their specific characters, as _Lates calcarifer_, species of _Dules_, _Plotosus anguillaris_; others (species of _Arius_) are but little different from Indian congeners. All these fishes must have migrated by the sea; a supposition which is supported by what we know of their habits. We need not add that India has not received a single addition to its freshwater fish-fauna from the Pacific region.