Salmo salar, Esox lucius, Acipenser sturio, A. maculosus, and several Petromyzonts.
2. Lates calcifer is common in India as well as in Queensland.
3. Galaxias attenuatus inhabits Tasmania, New Zealand, the Falkland Islands, and the South American continent.
B. Genera Identical in Distant Continents. 1. The genus Umbra, so peculiar a form as to be the type of a distinct family, comprises two most closely allied species only, one of which is found in the Atlantic States of North America, the other in the river system of the Danube.
2. A very distinct genus of Sturgeons, Scaphirhynchus, consisting of two species only; one of these inhabits the fresh waters of Central Asia, the other the system of the Mississippi.
3. A second most peculiar genus of Sturgeons, Polyodon, consists likewise of two species only, one inhabiting the Mississippi, the other the Yang-tse-Kiang.
4. Amiurus, A siluroid, and Catastomus, a Cyprinoid genus, both well represented in North America, have a single species each, in temperate China.
5. Lepidosiren is represented by one species in tropical America, and by the second in tropical Africa (Protopterus).
6. Galaxias is equally represented in South Australia, New Zealand and the southern parts of South America.
C. Families Identical in Distant Continents. 1. The Labyrinthici, represented in Africa by 5, and in India by 25 species.
2. The Chromides, represented in Africa by 25, in South America by 80 species.
3. The Characinidae, represented in Africa by 35, and in South America by 226 species.
4. The Haplochitonidae, represented in southern Australia by 1, in New Zealand by 1, and in Patagonia by a third species.
The facts regarding the distribution of freshwater fish show that it is not uncommon for identical families, genera and even species to be found living in rivers on opposite sides of the world without any known relatives in the intervening rivers. There seems to be no limit to the distance which freshwater fish may migrate in the same circumpolar zone; while even mountains, deserts, or oceans, do not offer absolute barriers. It is thus easy to see that migrations which would be impossible for marine forms offer no difficulties to freshwater organisms, and localized occurrences which would be inexplicable for
