108 THE UNIVERSITY SCIENCE BULLETIN. 



Genus GERRIS Fabr. 1794. 



This genus is our largest in the family. It contains 9 species, placed 

 in the two subgenera Aquarius and Gerris. The former with four 

 species, G. remigis, G. orba, G. conformis and G. robusta. The latter con- 

 tains G. gillettei, G. nnarginatus, G. argenticollis, G. biienoi, and G. can- 

 aliculatus. 



KEY TO GERRIS. 



A. First segment of antennse shorter than second and third together. 



Subg. Gerris. 

 B. Sixth abdominal segment acutely produced into a spine, com- 

 paratively slender species (mostly apterous). 



G. canaliculatus. 

 BB. Sixth abdominal segment not spinously produced, stouter 

 species (mostly winged). 



C. Anterior margin of pronotum with a flavous line; sec- 

 ond emargination of sixth male segment roundly rec- 

 tangular, female genital segment comparatively broad; 

 connexivum dark. G. buenoi. 



CC. Anterior margin of pronotum yellow clothed with thick 

 silvery pubescence. G. argenticollis, 



CCC. Anterior margin of pronotum concolorous; second 

 emargination of sixth male segment narrow and 

 rounded ; female genital segment comparatively nar- 

 row, connexivum flavus. G. marginatus. 

 (Note) Gerris gillettei L & S is omitted from this series 

 pending further study. 

 AA. First segment of antennas as long or longer than the second and 

 third together. Subg. Aquarius. 

 B. Comparatively stout bugs. The spines of sixth abdominal 

 segment not reaching end of genital plate. 

 C. Male venter, with two large blackish spots on each seg- 

 ment; male venter sulcate down the middle. Cr. ^e^^g';5 

 CC. Male venter without conspicuous black patches, shal- 

 lowly sulcate down the middle. G. robusta. 

 BB. Comparatively slender, generally winged, spines of sixth seg- 

 ment reaching end of genital segment. G. conformis. 

 (Note.) G. orba omitted for present. Van Duzee says he is 

 not sure he can tell it from remigis. 



Gerris remigis Say 1832. 



Say, Het. N. Harm., p. 35, 1832; Compl. writing Le Conte, vol. I, p. 362. 



"Dark olivaceous; thorax rounded behind, without an elevated line. 



"Inhabits United States. 



"Body dark brownish-olivaceous; thorax transversely rugulose without 

 much appearance of a dorsal raised line; a dull ochraceous and indented 

 line before; posterior margin regularly and obtusely rounded with but a 

 very narrow depressed margin; tergum with a black line on the middle, 

 in which is a series of obsolete gray lines; lateral margin with a series 

 of grayish points or short transverse lines; beneath with a silvery seri- 

 ceous reflection, an impressed line on the anterior part of the pectus 

 behind the anterior feet. 



"Length, half an inch. 



