CRUSTACEA OF FRESH WATERS 185 



These subterranean channels intercommunicate over 

 wide areas, and are now known in many parts of the 

 world to contain a peculiar assemblage of animals 

 which become accessible to the naturalist in wells and 

 in the streams and lakes of large caves. Further, 

 the scanty '* abyssal " fauna of deep lakes is partly 

 made up of species which enter the lakes by sub- 



FiG. 62 — A Well Shrimp {Niphargus aqidlex). x 7. (After 

 Wrzesniowski.) 



terranean channels, and find a suitable habitat in 

 the deep water. Species of Niphargus^ for example, 

 have been dredged in Lough Mask in Ireland and in 

 some of the Swiss lakes. 



Several species of blind Crayfishes have been found 

 in caves in North America, the best know^n being one 

 (Cambarus pelhicidus—Fl^te XXV.) found in the 

 Mammoth Cave in Kentucky; and blind Prawns 



