THE CliAYFl^n 133 



continuous genera ; that is, genera which now occupy widely 

 separated areas, like Astacus in Europe and Pacific North 

 America, but which once ranged over the intervening regions 

 as well. From some cause, the struggle for existence became 

 too severe in the intervening regions, so that Astacus and Cam- 

 barus were annihilated on the eastern and western sides of 

 the continents respectively. In southern Asia we find that the 

 struggle was doubtless with the successful river-crab. It is 

 interesting to note that, probably on account of the preserving 

 influence of climate, the other animals and the plants of the 

 eastern sides of the two continents and those of the western 

 sides are more alike than those from opposite sides of the same 

 continent. One of the best pieces of evidence for the conclu- 

 sion of a former hemispherical distribution of the two genera 

 of crayfishes is that there occur in the caves of Carniola in 

 southern Austria crayfishes ^ belonging to the genus Cambarus ; 

 — the only known living representatives of this type in 

 Europe. The mere fact that it lives in a cave is not sufficient 

 to make the crayfish Carniola of a Cambarus, for in North 

 America the genus has certainly not originated under the in- 

 fluence of subterranean life ; it is more likely that the caves of 

 Carniola have protected these crayfish from the widespread 

 destruction which has overwhelmed their fellows outside. 



Only one crayfish, Cambarus bartonii, is found in New England, 

 and here onlj^ in the rivers of Maine, Vermont, and central and west- 

 ern Massachusetts. The common species of the Midrlle States is 

 C. affinis. C. diogencs and C. immunis are common burrowing species 

 of the Central States. C. pcUucides is the blind species found in 

 Mammoth and W5'andotte caves. 



The food of the crayfish is verj' varied ; it may be living or 



' These crayfishes are blind, like the cave-inhabiting CamlDarus of America. 



