DISTRIBUTION 143 



in a well-boring near Basel. Since then various species of the Bathy- 

 nellacea have been found in Africa, Malaya, Japan and from the 

 mouth of the Amazon. It is probable that when more caves are 

 explored the various small Malacostraca will be found to be wide- 

 spread. Recent evidence for this view is the discovery of RJiopalo- 

 nurus holthuisi, a small peracaridan of uncertain affinities, which 

 was found in a cave in the West Indies. 



The Anaspidacea are larger relatives of the Bathynellacea; at the 

 present time they are confined to fresh waters in Tasmania and the 

 district around Melbourne in Australia, but in the past they were 

 more widespread, as evidenced by fossils from the Carboniferous 

 deposits of North America and Europe. 



The large number of species of the amphipod family Gam- 

 maridae in Lake Baikal has already been mentioned; other species 

 of the family are common in fresh waters in various parts of the 

 world. Another family, the Talitridae, has produced a small flock, 

 belonging to the genus Hyalella, in the fresh waters of South 

 America. Apart from these two families (which also have many 

 marine representatives) there are only occasional species from other 

 amphipod families which have taken to living in fresh water. 

 Corophium curvispinum is an example; this species lives in various 

 rivers in Europe, and in the northern parts of the Black and 

 Caspian Seas. It seems most probable that it migrated into the 

 rivers from these dilute seas. 



Isopods are best represented in fresh waters of the Northern 

 Hemisphere by members of the Asellidae, and less well by 

 occasional species from other families. The most important of these 

 families are the Sphaeromidae and the Cirolanidae. About a dozen 

 species of the former family, belonging to the genera Monolistra, 

 Microlistra and Caecosphaeroma, are known from fresh water in 

 caves of Europe. It is perhaps significant that the genus Sphaeroma 

 is particularly abundant in brackish water. 



A few parasitic isopods are known from fresh water, for instance, 

 Probopygrus bithynis is found as a parasite of the fresh-water 

 shrimp Macrobrachium in Central America. 



The Phreatoicidea are a peculiar group of isopods (fig. 58), 

 which at first sight look remarkably like amphipods; they are found 

 in the fresh waters of Australia, New Zealand and South Africa, 

 and may be thought of as the counterpart of the Asellidae in these 

 areas. 



Tanaidaceans do not seem to have taken to fresh water very well, 



