THE WHERRYMEN OR WATER STRIDERS. 969 



reappear on the first warm days of spring. The eggs are soon 

 after attached by a sort of glue to the leaves and stems of 

 aquatic plants. They hatch in about two weeks, the young 

 emerging from a slit which opens a little way down the side. 

 There are commonly two forms of the adult belonging to the 

 same species, the winged and unwinged. These do not neces- 

 sarily coexist. During some years only the winged forms ap- 

 pear, while in others, if the spring and summer are cool, all 

 will be unwinged. Often in sunny protected places where food 

 is abundant, all will be winged. 



The family is widely distributed, its members occurring in 

 all parts of the world, 19 species, distributed among six genera, 

 occurring in the eastern states. The principal literature treat- 

 ing of them is by Say, I, 362; Uhler, 1871, 1878; Champion, 

 1898; Kirkaldy, 1906; Bergroth, 1908; Bueno, 1911, 1915, 

 1917b, 1917c; Parshley, 1916; Riley, C. F., 1919, 1920, 1922, 

 1922a, and Hungerford, 1920. 



KEY TO EASTERN GENERA OF GERRID^E. 



a. Inner margin of the eyes concave or sinuate behind the middle; 

 body comparatively long and narrow, the abdomen long (Sub- 

 family Gerrinse). 



b. Pronotum sericeous, dull, in wingless forms fused with mesonotum; 



hind margins in winged form wide, obtusely rounded; basal 

 joint of front tarsi but little shorter than apical one. 



I. Gerris, p. 970. 

 bb. Pronotum glabrous, shining, in wingless form not fused with meso- 

 notum ; hind margin of latter in winged form narrowly rounded ; 

 basal joint of front tarsi much shorter than apical one. 



II. Limnogonus, p. 978. 

 aa. Inner margin of eyes convexly rounded; body short and broad; 

 pronotum in brachypterous form not fused with mesonotum ; abdo- 

 men usually very short (Subfamily Halobatinae). 



c. First antennal nearly or quite equal to the remaining three united, 



distinctly longer than 2 and 3 together; hind femora twice as 



long as hind tibia?. III. Metrobates, p. 980. 



cc. First antennal much shorter than the other three united, not much 



longer, sometimes shorter, than 2 and 3 together. 



d. Fourth antennal equal to or shorter than third; hind femora equal 



to or shorter than hind tibia and tarsus united; abdomen as long 



as remainder of body, strongly tapering toward apex. 



IV. Rheumatobates, p. 981. 



dd. Fourth antennal distinctly longer than third ; abdomen much 



shorter than remainder of body. 



e. Color black and yellow; eyes large, fairly prominent; lacustrine 



species. V. Trepobates, p. 985. 



