1. Africa has, in common with India, the Siluroid group of _Clariina_, the _Silurina_, and _Bagrina_; and more especially the small but very natural family of _Notopteridæ_, represented by three species in India, and by two on the _west coast_ of Africa. It would be hazardous to state at present in which of the two regions these fishes first made their appearance, but the discovery of remains of _Notopteridæ_ and _Silurina_ in tertiary deposits of Sumatra points to the Indian region as their original home. We can have less doubt about the other fishes common to both regions; they are clearly immigrants into Africa from the East, and it is a remarkable fact that these immigrants have penetrated to the most distant limits of Africa in the west as well as in the south,--viz. the _Labyrinthici_, represented by two genera closely allied to the Indian _Anabas_; the _Ophiocephalidæ_ and _Mastacembelidæ_, a few species of which have penetrated to the west coast, singularly enough being absent from the eastern rivers; the _Ariina_, represented by several species, of which one or two are identical with Indian, having extended their range along the intervening coasts to the east coast of Africa. The Cyprinoids also afford an instance of an Indian species ranging into Africa, viz. _Discognathus lamta_, which seems to have crossed at the southern extremity of the Red Sea, as it is found in the reservoirs at Aden and the hill-streams of the opposite coast-region of Abyssinia. 2. No such direct influx of species and genera has occurred from South America into Africa. Yet the affinity of their Freshwater fishes is striking. Two of the most natural families of fishes, the _Chromides_ and _Characinidæ_, are peculiar, and (with the exception of _Etroplus_) restricted to them. The African and South American Dipnoi are closely allied to each other. The _Pimelodina_, so characteristic of Tropical America, have three representatives in Africa, viz., _Pimelodus platychir_, _P. balayi_, and _Auchenoglanis biscutatus_; the _Doradina_ are another Siluroid group restricted to these two continents.[25] Yet, with all these points of close resemblance, the African and South American series are, with the exception of the two species of Pimelodus, _generically_ distinct; which shows that the separation of the continents must have been of an old date. On the other hand, the existence of so many similar forms on both sides of the Atlantic affords much support to the supposition that at a former period the distance between the present Atlantic continents was much less, and that the fishes which have diverged towards the East and West are descendants of a common stock which had its home in a region now submerged under some intervening part of that ocean. Be this as it may, it is evident that the physical conditions of Africa and South America have remained unchanged for a considerable period, and are still sufficiently alike to preserve the identity of a number of