THE BACK-SWIMMERS. 1049 



side margins oblique, feebly reflexed, hind margin sinuate, its 

 median portion usually truncate ; scutellum broadly triangular, 

 its apical portion acute, prolonged between the claval com- 

 missure ; elytra strongly tectiform ; clavus and corium wholly 

 coriaceous, without veins ; membrane nearly similar in texture, 

 without visible veins ; front and middle legs usually shorter and 

 stouter than the hind ones, the latter more slender, the inner 

 side of their tibiae and tarsi, except in Plea, with a dense fringe 

 of long hairs ; middle femora armed beneath near apex of outer 

 margin with a slender tooth, this usually followed by two or 

 three small tubercles or long setae; abdomen usually keeled at 

 middle, the keel as well as the sides of the ventrals with tufts 

 of long hairs. 



About 20 species of the family are known from North 

 America. They inhabit ponds, lakes and pools of stagnant wa- 

 ter in ditches and streams, some of the species being abundant 

 in the masses of submerged water weeds close to the shores. 

 Of their habits Uhler (1884, 252) says: 



"All are capable of sustained flight and often go long distances in 

 search of a congenial body of water when the food gives out or the water 

 shallows in the place where they were born. The incessant activity of 

 these insects in the water is very remarkable; from early morning until 

 sundown and even later they are rising with sudden jerks from the 

 bottom to the surface, and then diving with the hind legs in rapid motion. 

 A spray of grass or projecting stick at the top of the water serves as 

 a balancing point by which to sustain themselves at pleasure. Their 

 appetite, also, seems almost insatiable. Every insect they can overcome 

 falls a prey to their quick grasp and is held with unbending tightness 

 until its fluids are completely withdrawn. If not picked up with caution 

 they take the first opportunity to plunge their beak deeply into the flesh, 

 producing a keenly smarting pain which lasts for several minutes." 



The principal literature treating of our 16 eastern species is 

 by Uhler, 1878, 1884; Kirkaldy, 1897; Champion, 1901; Bueno, 

 1902, 1905a, 1907b, 1909a; Hungerford, 1917, 1917a, 1917b, 

 1917c, 1918, 1920, 1923a, 1924a, and Bare, 1925. They are dis- 

 tributed among two subfamilies and three genera. 



KEY TO EASTERN* GENERA OF NOTONECTl O.K. 



a. Hind legs longer than the others, their tibia? and tarsi with a fringe 

 of long hairs; abdomen keeled and hairy; eyes very large and con- 

 spicuous; length, 5 or more mm. (Subfamily Notonectinae). 

 b. Elytra pubescent; last antennal joint much shorter than the one 

 preceding; scutellum almost as long as claval commissure. 



I. Notonecta, p. 1050. 



