204 THE HABITAT OF THE EURYPTERIDA 



Salmo salar, Esox lucius, Acipenser sturio, A. maculosus, and several 

 Petromyzonts. 



2. Lates calcifer is common in India as weD as in Queensland. 



3. Galaxias attenuatus inhabits Tasmania, New Zealand, the 

 Falkland Islands, and the South American continent. 



B. Genera Identical in Distant Continents, i. The genus 

 Umbra, so peculiar a form as to be the type of a distinct family, com- 

 prises 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 , consist- 

 ing of two species only; one of these inhabits the fresh waters of Cen- 

 tral 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 Zea- 

 land and the southern parts of South America. 



C. Families Identical in Distant Continents, i. The Laby- 

 rinthici, 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 



