CYCL0PID2E. 89 



in the absence of a secondary branch from the 

 lower antennae, and in the conformation of the fifth 

 pair of feet, which are rudimentary, and alike in both 

 sexes, those of the male not being used as clasping 

 organs. The presence of two ovisacs in the female is 

 another distinctive character. From Haiyactidce the 

 family is distinguished mainly by the conformation of 

 the foot-jaws and first pair of swimming feet, all of 

 which in the latter family form powerful clawed pre- 

 hensile organs ; other less conspicuous differences, 

 however, occur, as in the structure of the lower 

 antennae and the fifth pair of feet. The family at 

 present includes only five British genera, one of which 

 {Cyclops) is confined to fresh water; the rest are 

 exclusively marine. 



Diagnosis of Genera of Cyclojoidce, 



rudimentary, reduced to f prehensile ; with uncinate 

 a tubercle bearing two \ terminal claws Thorellia. 



ft 



ft 



I 



branchial filaments. 



Lower foot-jaw V. not prehensile Cyclops, 



f many joints Oithona. 



two-branched, 



secondary branch -j one joint; ") foliaceous Lophophorus. 



composed of | fifth pair of > 2- or 3-jointed, 



(^ feet J cylindrical . . . Cyclopina. 



