hungerford: aquatic hemiptera. 107 



the Diptera was probably applied to some of these bugs. The Gerrids are 

 allied to the Veliids and have often been placed together, with others, in 

 the family Hydrometridse. 



KEY TO THE GENERA OF GERRID-E. 



A. Inner margin of the eyes accurately sinuate behind the middle. 

 Body comparatively long and narrow, abdomen long. 

 B. Pronotum sericeous, dull, antennae comparatively short and 

 stout. 

 C. First segment of the antennae shorter than the second, 

 and third taken together. 

 D. Antennae as long as half the body; sixth abdominal 

 segment of the male roundly emarginate. 



Limnoporus. 

 (1 species.) 



DD. Antennae not as long as half the entire length of 

 the insect, not extending beyond the thorax; sixth 

 abdominal segment of male doubly emarginate. 



Gerris. 



(9 species.) 



CC. First segment of the antennae longer than the second 

 and third taken together. Gerris. 



(subgenus Aquarius.) 



(4 species.) 



BB. Pronotum glabi-ous, shining; antennae long and slender. 



Tenagogonus. 



(3 species.) 



AA. Inner margin of the eyes convexly rounded; body comparatively 

 short and broad, abdomen so short as to appear almost nymphal in 

 some forms. 

 B. First antennal segment much shorter than the other three 

 taken together; not much longer than the second and third 

 taken together, and sometimes shorter. 

 C. Fourth (apical) segment of antennae longer than the 

 third. 

 D. Eyes larger, fairly prominent; colors black and 

 yellow. Trepobates. 



(1 species.) 



DD. Eyes smaller, widely separated; plumbeous forms, 

 entirely sericeous. Halobates. 



(2 species. Ocean dwellers.) 



CC. Fourth segment of antennae never more than equal to 

 third ; basal segment of anterior tarsi much shorter than 

 second; hind femur equal to or much shorter than hind 

 tibia and tarsus taken together. Rheumatobates. 



(3 species.) 



BB. First antennal segment nearly equal to the remaining three 

 taken together, much longer than second and third; antennae 

 almost as long as entire body; hind femora twice as long as 

 hind tibia. Metrobates. 



(1 species.) 



