CYCLOPS. 103 



the cephalo thorax, broad at the base, and tapering 

 gradually to the extremity ; last three joints long and 

 slender and bearing a simple untoothed longitudinal 

 ridge ; first, fourth, and seventh joints larger than 

 the rest, clothed on the outer margin, more espe- 

 cially near the base, with long hairs. Posterior 

 antennae very slender j the last two joints of 

 about equal length, the second shorter and finely 

 setose on the lower margin. Fifth foot (fig. 7) 

 2- jointed, first joint large and having one long 

 apical seta, second smaller, with one very long 

 and one small seta, and terminating in a small 

 process, which is provided with one long slender seta. 

 Caudal segments about twice as long as broad, some- 

 what longer than the preceding abdominal segment. 

 Longest of the tail setae (fig. 8) about equal in length 

 to the abdomen, densely plumose, as also are the setas 

 of the swimming feet. Ovisacs irregularly shaped and 

 and adpressed. Length -^-th of an inch (2'55 mm.). 



G. tenuicornis is a very abundant species, occurring 

 in lakes, ponds, and ditches, throughout England, 

 Scotland, and Ireland; it appears to be of equally 

 common occurrence on the Continent of Europe, and 

 is very nearly allied to G. signatus, from which, how- 

 ever, it is distinguishable at once by the characters of 

 the antennas. 



