Occasional Papers of ihc Museum of Zoology 15 



sweeping the sedges and by j)icking the insects frdm the sur- 

 face of the water, where they had probably been driven from 

 the Carex by the strong wind which was blowing at the time. 



Family Xotoxectidae^ thk Back-swim. afers 



Key to the Genera of Xotoueetidae of the Douglas Lake Region 



1. Hind tibiae and tarsi not ciliated; abdomen not keeled; body 



about twice as long as wide, roundly convex above ; length 



less than 3 mm Plea 



Hind tibiae and tarsi ciliated; abdomen keeled and hairy; 

 body two and one-half to three times as long as wide, much 

 less convex above ; length 5 mm. or more 2 



2. Fourth antennal segment much longer than third ; hind tarsi 



with minute claws; length less than 8 mm., shape slender. BuEXO-\ 

 Fourth antennal segment much shorter than third ; hind tarsi 

 without claws ; length more than 8 mm., shape more 

 robust NoToNECT.v 



Genus Notoxecta Linnaeus 



In the following key to the species of Xotonecta the term 

 vertex means the anterior edge of the head between the eyes 

 as seen from above, and the term synthlipsis is applied to the 

 place on the dorsal side of the head, near the hind margin of 

 the eyes, where the interocular distance is a minimum. 



Key to the Speeies of Au)toneeta in the Douglas Lake Region 



1. Inner margins of the eyes not greatly diverging, vertex not 



more than one and one-half times as wide as synthlipsis ; 



length about 14 mm., coloration variable iV. insulata 



Inner margins of eyes more widely divergent, verte.x at least 



twice as wide as synthlipsis 2 



2. Vertex two to two and one-half times as synthlipsis 3 



Vertex three times as wide as .synthlipsis 4 



3. Larger species, length 123^-14 mm.; body more robust, 



length about 2.7 times width of pronotum ; color luteous, 

 scutellum nearly concolorous with hemelytra, which are 

 rarely marked with dark except for a short narrow margin- 

 al vitta at base of costal area .V. borcalis 



