J. R. DE LA TORRE BUENO. 245 



(Only one species of this genus, Gerris {Limnogonus) hyaliniis Fabr. 

 is recorded from the United States. It extends south from Florida 

 throughout South America.) 



Key to subgenus Gerris S. str. {^^ Liinnotreclms Stal). 



1. (2.) Sixth abdominal segment acutely produced into a spine, com- 



paratively slender species, is found mostly apterous. 



canaliciilatus Say. 



2. (1.) Sixth abdominal segment not spinously produced, stouter 



species, mostly winged. 



3. (4.) Anterior margin of pronotum with a flavous line; second 



emargination of sixth 6^ segment roundly rectangular , 9 

 genital segment comparatively broad ; connexivum dark. 



bueiioi Kirk. 



4. (3). Anterior margin of the pronotum concolorous ; second emar- 



gination of sixth cf segment narrow and rounded ; 9 geni- 

 tal segment comparatively narrow, connexivum flavus. 



inarginatus Say. 



Key to subgenus Aquarius Schell. {^^ Hygrotrechtis Stal). 



1. (2.) Comparatively stout species, generally apterous ; legs short ; 



underside of body dark ; spines of sixth abdominal segment 

 not reaching end of genital segment reiuig'is Say. 



2. (1.) Comparatively slender, generally winged ; legs long ; under- 



side of body yellowish ; spines of sixth segment reaching end 

 of genital segment coiifoi'inis Uhler. 



Key to tribe Halobatini. 



1. (6.) First antennal joint much shorter than the other three taken 



together ; not much longer than the second and third taken 

 together, and sometimes shorter. 



2. (5,) Fourth (apical) joint longer than third. 



3. (4.) Eyes larger, fairly prominent ; colors black and yellow ; lacus- 



trine species. 



Genus Trepobates Uhler (= Stephania F. B. White). 

 (One species thus far recognized, of great distribution, Trebobates 

 pictiis H. S.) 



4. (3.) Eyes small, widely separated; plumbeous forms, entirely 



sericeous ; oceanic forms Genus Halobates Esch. 



(Thus far, one species only appears to have been found on our 

 coasts, H. micans Esch., which at times is found on the Florida 

 beaches.) 



5. (2.) Fourth (apical) joint never more than equal to third ; basal 



joint of anterior tarsi much shorter than second ; hind femora 

 equal to or much shorter than hind tibia and tarsus taken 

 together Genus Rlieuiuatobates Bergr. 



TRANS. AM. ENT. SOC, XXXVII. 



