ENTOMOSTRACA. 203 



ment, being almost constantly in motion, either swimming 

 about rapidly by the action of their antennae, or walking 

 upon the plants and other solid bodies floating in the water. 

 Instead of being fixed in one place, and condemned to live 

 amidst eternal darkness, like the molluscous. animals to which 

 they bear such striking resemblance in external covering," 

 " they," to use the words of Miiller, " by opening their 

 valves enjoy hght and move at their will, sometimes bury- 

 ing themselves in the mud, sometimes darting through the 

 water, the humid air of their atmosphere. If they meet any 

 unforeseen object, they conceal themselves all at once in 

 their shells and shut the valves, so that force and address 

 seek to open them in vain." Cz/jyris having two pairs of feet 

 has been called a " quadruped crustacean ;" but the Cytliere 

 has three pairs of feet. The former belong to fresh water, 

 the latter are mostly marine ; the former swim, but the latter 

 do not ; they walk among the branches or leaves of Confervce 

 or Fuel, where they delight to dwell. When shaken out 

 from their hiding-places into a bottle or tumbler of water, 

 they may be seen to fall in gyrations to the bottom, without 

 ever attempting to dart through the w^atery element, as is 

 the case with the Cij prides. Upon reaching the bottom they 

 open their shells and creep along the surface of the glass ; 



