CRUSTACEA OF FRESH WATERS 179 



of Engceus (Plate XX.), found in Tasmania, are there 

 known as " Land Crabs," and burrow in marshy 

 places and in the forests up to an elevation of 

 4,000 feet. 



The broad equatorial belt which separates the 

 regions inhabited by the Northern and the Southern 

 Crayfishes is characterized by the presence of several 

 other groups of fresh-water Decapoda. The large 

 River Prawns, which are found nearly every- 

 where within the tropics, belong to the genus 

 Palcemon (Plate XXL), which is very closely related 

 to the common marine Prawns (Leander) of our own 

 coasts. Some of these Prawns grow to a foot or 

 more in length of body, and the large claws may 

 measure as much again. From the Crayfishes, for 

 which they are sometimes mistaken, they may be 

 easily distinguished by the fact that the large pincer- 

 claws are not the first, but the second pair of legs. 

 Another widely-spread group of River Prawns, for 

 the most part of small size, is the family Atyidae 

 (Plate XXII. ), in which the two pairs of pincer- 

 claws are feeble, and have the fingers tipped with 

 brushes of long hairs, used in sweeping up minute 

 particles of food from the mud. The distribution of 

 these Prawns presents many difficult problems, as an 

 example of which we may mention the presence of 

 identical or closely related species in the fresh waters 

 of West Africa and of the West Indies. 



The Brachyura (or Crabs) include many species 



