The Geographical Distribution of Fishes 251 



basins of China and the Eastern United States, as compared with 

 those of Europe or the Californian region. 



Minor divisions are those which separate the Great Lake 

 region from the streams tributary to the Gulf of Mexico; and 

 in Asia, those which separate China from tributaries of the 

 Caspian, the Black, and the Mediterranean. 



Equatorial Zone. The Equatorial Zone is roughly indicated 

 by the tropics of Cancer and Capricorn. Its essential feature 

 is that of the temperature, and the peculiarities of its divisions 

 are caused by barriers of sea or mountains. 



Dr. Giinther finds the best line of separation into two 

 divisions to lie in the presence or absence of the great group 

 of dace or minnows,* to which nearly half of the species of fresh- 

 water fishes the world over belong. The entire group, now 

 spread everywhere except in the Arctic, South America, Aus- 

 tralia, and the islands of the Pacific, seems to have had its 

 origin in India, from which region its genera have radiated in 

 every direction. 



The Cyprinoid division of the Equatorial Zone forms two 

 districts, the Indian and the African. The Acyprinoid division 

 includes South America, south of Mexico, and all the islands of 

 the tropical Pacific lying to the east of Wallace's line. This 

 line, separating Borneo from Celebes and Bali from Lompoe, 

 marks in the Pacific the western limit of Cyprinoid fishes, as 

 well as that of monkeys and other important groups of land 

 animals. This line, recognized as very important in the distribu- 

 tion of land animals, coincides in general with the ocean current 

 between Celebes and Papua, which is one of the sources of the 

 Kuro Shiwo. 



In Australia, Hawaii, and Polynesia generally, the fresh- 

 water fishes are derived from marine types by modification of 

 one sort or another. In no case, so far as I know, in any island 

 to the eastward of Borneo, is found any species derived from 

 fresh-water families of either the Eastern or the Western Conti- 

 nent. Of course, minor subdivisions in these districts are formed 

 by the contour lines of river basins. The fishes of the Nile differ 

 from those of the Niger or the Congo, or of the streams of Mada- 



* Cyprinidae. 



