FISHES OF LAKE SUPERIOR. 265 



in number. There are also some on the Atlantic shores of North 

 America, along the British Possessions as well as the Northern and' 

 Middle United States. They seem to be exceedingly numerous in 

 the northern Pacific, being found everywhere from Behring's Straits 

 and Japan to the northern shores of China, and on the north-west 

 coast of America, as far south as the Columbia River. Again, the 

 so called western waters of the United States have their own 

 species, from the Ohio down to the lower portion of the Mississippi, 

 but it does not appear that these species ascend the rivers from the 

 Gulf of Mexico. I suppose them to be rather entirely fluviatile, like 

 those of the great Canadian lakes. 



Beyond the above limits southwards there are nowhere sturgeons 

 to be found, not even in the Nile, though emptying into a sea in 

 which they occur ; and as for the great rivers of Southern Asia and 

 of tropical Africa, not only the sturgeons, but another flimily is 

 wanting there, I mean the family of Goniodonts which in Central 

 and Southern America takes the place of the sturgeons of the 

 North. Again, all the species in different parts of the world are 

 different. 



It is a most extraordinary fact, which Avill hereafter throw much 

 light upon the laws of geographical distribution of animals and their 

 mode of association, viz., that certain families are entirely circum- 

 scribed within comparatively narrow limits, and that their special 

 location has an unquestionable reference to the location of other ani- 

 mals ; or in other words, that natural families, apparently little related 

 to each other, are confined to different parts of the world, but are 

 linked together by some intermediate form, which itself is located in 

 the intermediate track between the two extremes. In the case now 

 before us, we have the sturgeons extending all around the world in 

 the northern temperate hemisphere, in its seas as well as in its fresh 

 waters, all closely related to each other. Neither in Asia nor in 

 Africa is there an aberrant form of that type, or any representative 

 type in the warmer zones ; but in North America we have the 

 genus Scaphirhynchus, which occurs in the Ohio and Mississippi, and 

 which forms a most natural link with the family of Goniodonts, all the 

 species of which are confined exclusively to the fresh waters of 

 Central and South America. The closeness of this connection will be 



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