244 HETEROPTERA. 



3. (2.) Head normal, not greatly produced beyond eyes. 



4. (5.) Antennae moderately long and slender, four-jointed, bugs of 



moderate size (about 5 mm.), winged or wingless, body gen- 

 erally green in color Family MESOVELIID^. 



5. (4.) Antennae short and comparatively stout, 5-jointed, last joint 



fusiform, minute species (less than 3 mm.), winged or 

 (rarely) wingless Family N^OGEID^. 



6. (1.) Claws subapical at least in one pair of feet. 



Family GERRID^. 



7. (10.) Posterior femora extending beyond the abdominal apex. 



Subfamily Gerrin^. 



8. (9.) Inner margin of the eyes convexly rounded ; body compara- 



tively short and broad, abdomen so short as to appear almost 

 nymphal in some forms Tribe Halobaihii. 



9. (8.) Inner margin of the eyes accurately sinuate behind the mid- 



dle ; body comparatively long and narrow, abdomen long. 



Tribe Gerrini. 

 10. (9.) Posterior femora not extending to the abdominal apex. 



Subfamily Veliin^. 



In the tribe Gerrini, thus far only one genus has appar- 

 ently been recorded east of the Mississippi and north of 

 Georgia. This is the genus Gerris, consisting of three sub- 

 genera held by some authors to be genera. The characters 

 of the tribe as given above will serve to distinguish the 

 genus, and the following key will help to separate the sub- 

 genera : 



Genus GERRIS Fabricius. 



1. (6). Pronotum sericerous, dull, antenna; comparatively short and 



stout. 



2. (5). First joint of the antennae shorter than the second and third 



taken together. 



3. (4). Antennae as long as half the body; sixth abdominal segment 



in the cf roundly emarginate. 



Subgenus Liiiiinoporoiis Stdl. 

 (One species, Gerris {Lhnnoporns) rufoscutellatus Latreille. 



4. (3). Antennae not as long as half the entire length of the insect, 



not extending beyond the thorax ; sixth abdominal segment 

 in c? doubly emarginate. 



Subgenus Gerris s. str. (= Linmotrechus Stdl). 



5. (2). First joint of the antennae longer than the second and third 



taken together. 



Subgenus Aquarius Schell. (= Hygrotrechus Stdl). 



6. (1). Pronotum glabrous, shining; antennae long and slender. 



Subgenus Liinnog'onus Stdl. 



