30 THE UNIVERSITY SCIENCE BULLETIN. 



AAA, Coursing upon the water by quick, jerky movements — Concluded. 



DD. Small, dark insects, with long, slender legs. 



Gerridse. 

 (genus Rheumatabates.) 

 CC. On moderately rapid streams or little bays and 

 eddies connected therewith. Veliidse. 



(genus Velia.) 

 CCC. On the riffles and rapids. Veliidm. 



(genus Rhagovelia.) 

 BB. Marine. Sometimes far from land.^*-'^^'^'^*' V a jowrftg . 



(genus Halobates.) 

 AAAA. Living within the water. 



B. Clinging to supports and remaining in contact with sur- 

 face film. 



C. With long respiratory tube at caudal end. 



Nepidie. 

 D. In tangled trash (elongate). 



(genus Ranatra.) 

 DD. In the mud and trash; broad, flat. 



(genus Nepa.) 

 CC. With short, retractile respiratory tube at caudal 

 end Belostomatidse 



D. Length 1 inch or less, often carrying egg 

 clusters in summer. 



(genus Belostoma.) 



DD. Length, 1% inch or more. 



E. Very large bugs, with fore femora 

 grooved. (genus Lethocerus.) 



EE. Very large bugs, with fore femora not 

 grooved. (genus Benacus.) 



BB. Free swimming. 



C. Swimming upon their backs, often resting with 

 tip of abdomen at surface. Notonectidse. 



D. Very tiny, plump, little creatures, found 

 clinging to aquatic plants. 



(genus Plea.) 

 DD. Larger forms. 



E. Slender bugs, with eyes parallel, dwell- 

 ing for most part in open waters, 

 where they swim submerged. 



(genus Biienoa.) 



EE. More robust bugs, resting with tip of 

 abdomen at surface or clinging to sub- 

 merged vegetation. 



(genus Notonecta.) 



