Ophiocephalus, again, is a truly Indian genus, there being no less than twenty-five species,[[145]] all from the fresh waters of the East Indies. Yet Dr. Günther informs me that there is a species in the Upper Nile and in West Africa.
The acanthopterygian family (Labyrinthici) contains nine freshwater genera, and these are distributed between the East Indies and South and Central Africa.
The Carp fishes (Cyprinoids) are found in India, Africa, and Madagascar, but there are none in South America.
Thus existing fresh-water fishes point to an immediate connexion between Africa and India, harmonizing with what we learn from Miocene mammalian remains.
On the other hand, the Characinidæ (a family of the physostomous fishes) are found in Africa and South America, and not in India, and even its component groups are so distributed,—namely, the Tetragonopterina[[146]] and the Hydrocyonina.[[147]]
Again, we have similar phenomena in that almost exclusively fresh-water group the Siluroids.
Thus the genera Clarias[[148]] and Heterobranchus[[149]] are found both
in Africa and the East Indies. Plotosus is found in Africa, India, and Australia, and the species P. anguillaris[[150]] has been brought from both China and Moreton Bay. Here, therefore, we have the same species in two distinct geographical regions. It is however a coast fish, which, though entering rivers, yet lives in the sea.
Eutropius[[151]] is an African genus, but E. obtusirostris comes from India. On the other hand, Amiurus is a North American form; but one species, A. cantonensis,[[152]] comes from China.
The genus Galaxias[[153]] has at least one species common to New Zealand and South America, and one common to South America and Tasmania. In this genus we thus have an absolutely and completely fresh-water form of the very same species distributed between different and distinct geographical regions.