THE BACK-SWIMMERS. 



1051 



._,«_ Distance between 

 eyes at front 



Distance between 

 eyes at vertex 



Fig. 212. Dors;<] \iru of Notonecta irrorata I'lii.. showing structures, X 5. 

 (After Garman, Hemlptera of Connecticut). 



c. Scutellum black; greatest width of interocular area less than one 

 and a half times that of narrowest point; form less robust. 



1189. INSULATA. 



cc. Scutellum pale yellow, nearly concolorous with the elytra; greatest 



width of interocular area about twice that of narrowest point; 



form very robust. 1190. BOREALIS. 



aa. Smaller species, rarely over 11.5 mm. 



d. Greatest width of interocular area not more than three times that 

 of the narrowest point. 

 e. Pronotum less than twice as wide as long; greatest width of vertex 

 twice that of its narrowest part. 1191. howardi. 



ee. Pronotum twice or more as wide as long; greatest width of vertex 

 more than twice that of its narrowest point. 

 /. Form subrobust; color dull yellow, usually with distinct black 

 markings; greatest interocular width about two and one-third 

 times that of narrowest point; length, 10 — 11.5 mm. 



1192. UNDULATA. 



//. Form more slender; color dull white, often with faint dark mark- 

 ings ; gi-eatest interocular width about three times that of nar- 

 rowest point; length, 8 — 10 mm. 1193. variabilis. 

 dd. Greatest width of interocular area six or more times that of nar- 

 rowest point. 

 g. Scutellum black, elytra reddish-brown; length, 10 — 11.5 mm. 



1194. UHLERI. 



gg. Scutellum dull yellow, elytra paler; length, 8 — 9 mm. 



1195. RALEIGH I. 



