100 ZOOLOGY 



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 con- 

 clusion of a former hemispherical distribution of the two 

 genera of crayfishes is that there occur in the caves of 

 Carniola in southern Austria crayfishes l 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 Carniola crayfish a Cam- 

 barus, for in North America the genus has certainly not 

 originated under the influence of subterranean life ; it is 

 more likely that the caves of Carniola have protected these 

 crayfish from the widespread destruction which has over- 

 whelmed their fellows outside. 



Only one crayfish, Cambarus Bartonii, is found in New England., 

 and here, with two or three local exceptions, only in the rivers of 

 Maine. This C. Bartonii has the widest geographical distribution of 

 all the northern species. C. Blanding'd is the most widely distributed 

 of the southern species. C. pellucides is the blind species found in 

 Mammoth and Wyandotte caves. 



The lobster (Homarus) is, as we have already seen, the 

 nearest living salt-water relative of the crayfish. There 

 are only two species of the genus Homarus. One, Homarus 

 americanus, occurs on our Atlantic coast, the other, 

 H. vulyaris, is the lobster of Europe. On our Pacific 

 coast there is the "spiny lobster," but this is not closely 

 related to the eastern lobster (Fig. 95). The national gov- 



1 These crayfishes are blind, like the cave-inhabiting Cambarus of 

 America. 



