DISPERSION OF FRESH-WATER FISHES. 103 



The Killifishes have their greatest abundance in 

 tropical America, which is perhaps the place of 

 their origin. They are especially fishes of the 

 brackish waters, rarely going far out to sea. 

 Some of them ascend streams; and these fre- 

 quent spring waters, and waters which are clear 

 and cold. 



The two species of Mud-minnow are now very 

 widely separated as to habitat, although very simi- 

 lar to each other in structure. The one belongs 

 properly to our Great Lake Fauna, the other to 

 the streams of Austria. The two are probably re- 

 mains of a past fauna, in which the group was 

 more fully represented. Our Mud-minnow 1 is one 

 of the most tenacious of life of all our fishes, and 

 will often live for weeks in damp muck after the 

 waters of a pond have evaporated. 



Of the five known species of Pike, one is cos- 

 mopolitan, being spread over northern Asia and 

 Europe as well as America, while the other species 

 are somewhat restricted in their range. The Com- 

 mon Pike 2 is probably the parent stock of all ; but 

 whether originally American or not, we cannot 

 say. The affinities of the Mud-minnow with the 

 Pike are not remote, and doubtless forms between 

 the two have existed. 



The Black-fish* of Alaska is another relative of 

 the Mud-minnow and Pike. The single known 

 species is found in Alaska and eastern Siberia. 

 It too is probably an isolated relic of a disap- 

 pearing group. 



1 Umbra limi Kirtland. 2 Esox lucins Linnaeus. 



8 Dallia pectoralis Bean. 



