THE AQUATIC HETEROPTERA. 1019 



the water, others living therein throughout most of their days, 

 quitting it only to extend their foraging grounds through 

 flight. Those Heteroptera which are mainly aquatic in habitat 

 belong to the suborder Cryptocerata, so named from their hav- 

 ing the antennae present but usually very short and concealed 

 in grooves or cavities on the under side of the head (fig. 

 207, b). In addition they have the texture of the body largely 

 coriaceous and usually devoid of pubescence ; front legs more 

 or less raptorial or fitted for grasping and holding prey ; middle 

 and hind ones often greatly modified for rapid swimming, the 

 hind coxae being broad, more or less flattened and usually 

 hinged to the metasternum, the hind femora often flattened 

 and grooved for the reception of the tibiae in repose, both 

 femora and tibiae often fringed with hairs. 



To the suborder, as thus briefly defined, belong seven 

 families, separated as follows : 



KEY TO FAMILIES OF SUBORDER CRYPTOCERATA. 



a. Ocelli present; hygrophilous ; predaceous. 



b. Antennas exposed; front and middle legs similar; hind tarsi 2- 



jointed ; beak reaching or surpassing hind coxae. 



Family XXXIV. Ochterid^e, p. 1020. 

 bb. Antenna? concealed; front legs raptorial; eyes protuberant; beak 

 very short, concealed by front femora. 



Family XXXV. Nerthrid^e, p. 1022. 

 act. Ocelli absent; aquatic; usually predaceous. 



c. Hind tarsi with two distinct claws; beak 3-jointed. 

 d. Membrane of elytra without veins. 



Family XXXVI. Naucorid^e, p. 1029. 

 dd. Membrane with reticulate veins. 



e. Apical appendages of abdomen long and slender, not retractile; 

 tarsi 1-jointed; hind coxa? rotatory; body usually long and 

 very slender. Family XXXVII. Nepid^e, p. 1032. 



ee. Apical appendages of abdomen short and flat, retractile; tarsi 2- 

 jointed; hind legs distinctly flattened, the coxa? hinged; body 

 broad and flat. Family XXXVIII. Belostomatid^e, p. 1041. 

 cc. Hind tarsi without distinct claws." 



/. Base of head inserted in thorax; front tarsi 2-jointed, of males 

 sometimes 1-jointed; body convex and obtusely keeled above, so 

 that they swim back downward ; predaceous. 



Family XXXIX. Notonectid^e, p. 1048. 

 ff. Base of head overlapping apex of pronotum; front tarsi 1-jointed, 

 palaeform; body subdepressed above, so that they swim nor- 

 mally; apical ventrals of male asymmetrical; phytophagous, 

 feeding on aquatic plants. Family XL. Corixid^e, p. 1062. 



""Except in the genus Pica, whose members are less than 3 mm. in length. 



