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 crayfishes 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 still 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 all belong to the genus 
Cambarus (fig. 63, p. 248). Species of this genus also 
occur in Cuba,t 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 Cambari has 
been described by Dr. Hagen; and a blind Cambarus 
* Dr. Hagen in his “ Monograph of the North American Astacide,” 
enumerates six species; A. Gambelii, A. hlamathensis, A. leenisculus, 
A, nigrescens, A. oreganus, and A, Trowbridgii. 
+ Von Martens. Cambarus cubensis, Archiv. fiir Naturgeschichte, 
xxxviii. 
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