fflGHER CRUSTACEANS (MALyoMK.U A g,^ 



and logs, in holes, or among vegetation. But they arc present 

 practically everywhere, and in most budies of water, even 

 ones, one or several forms may be expected to occur. C". 

 forms (burrowing crayfishes) do not Ii\f iu opcFi water, but burrow 

 in the ground, going down to the groimd-waicT; their presence i^ 

 indicated by piles of mud, brought out of the holes. 



Fresh-water Malacostraca are found, with exception of the An- 

 tarctic regions, practically all over the world, including the Arctic. 

 but naturally are most abundant in the tropics. A numU-r of 

 groups are distinctly characteristic of temperate climates, and al 

 least one group (genus Cambarus, crayfish) has reached its hiKhesl 

 development in North America. Here Malacostraca an- found 

 ever3rwhere, but chiefly in the interior basin with its >;rcat and 

 diversified river systems. They become rather scarce on the west- 

 ern plains and in the arid regions, but are not entirely nW 

 there. The various forms are adapted to dilTerent surroumi...,. . 

 some prefer large rivers, others creeks or jx)nds. or small |)ools. 

 springs, and even subterranean waters. 



They belong to very difTerent groups of the subclas> .Ma! 

 traca. The latter has been divided, in the more recent sy>; 

 into ten orders, and of these four possess representatives in our 

 fresh waters: Isopoda, Amphipoda. Mysidacea. and Deca: 

 These differ very much in their outer features, in general - . 

 of body, size, color, and details of mori)hology, so that it is hard 

 to give a short general account of their characters. 



The body may be only a few millimeters long. u|) to one or two 

 centimeters (Isopods, Amphipods), or it ma\- be somewhat longer 

 (Mysidacea and some Decapods), while in otlur cases (prawns and 

 crayfishes among the Decapods) it may reach the considerable 

 length of ten centimeters and over. In tlu- smaller forms, ihe 

 color is generally inconspicuous, whitish or gra>ish. often more or 

 less transparent. The larger forms have more distinct color*. 

 which may become quite brilliant in certain parts of the IkkIv: the 

 large claws of the genus PaJjcmon (prawns) are. in the male sex. 

 often red, blue or purple. The crayfishes are. in genenU. of j^tx-n- 



ish or brownish olive tints, but as a nde adult mak^ an '- 



vividly colored, and in some species the adult male assumc-s a 



