NORTH AMERICAN CRAYFISHES. 305 



Thus, on the continent of the old world, the crayfishes 

 are restricted to a zone, the southern limit of which 

 coincides with certain great geographical features ; on 

 the west, the Mediterranean, with its continuation, the 

 Black Sea ; then the range of the Caucasus, followed by 

 the great Asiatic highlands, as far as the Corea on the 

 east. On the north, though there is no such physical 

 boundary, the crayfishes appear to be entirely excluded 

 from the Siberian river basins ; while east and west, 

 though a sea-barrier exists, the craj'fishes extend beyond 

 it, to reach the British islands and those of Japan. 



Crossing the Pacific, we meet with some half-a-dozen 

 kinds of crayfishes,* different from those of the old 

 world, but stiU belonging to the genus Astacus, in 

 British Columbia, Oregon, and California. Beyond the 

 Rocky Mountains, from the Great Lakes to Guatemala, 

 crayfishes abound, as many as thirty-two different species 

 having been described, but they aU belong to the genus 

 Camharus (fig. 63, p. 248). Species of this genus also 

 occur in Cuba,+ but, so far as is at present known, not 

 in any of the other West Indian islands. The occurrence 

 of a curious dimorphism among the male Camhari has 

 been described by Dr. Hagen; and a blind Camharus 



* Dr. Hagen in his " Monograph of the North American Astacldae," 

 enumerates six species ; A. Ga/mbelii, A. Tdamatliensin, A. leenisculiis, 

 A . nigresoens, A. oreganns, and A. Tromiridgii. 



f Von Martens. Canibarus culensis. Aichiv. fiir Naturgeschichte, 

 xxxviii. 



