AQUATIC INSECTS 



937 



21 (20) Ocelli wanting 22 



22 (23) Front tibiae with three spurs Family POLYCENTROPIDAE. 



23 (22) Spurs of the front tibiae fewer than three 24 



24 (25) Anterior branch of the radial sector in the fore wing forked. 



Family HYDROPSYCHIDAE. 



25 (24) Anterior branch of the radial sector simple. 



Family PSYCHOMYHDAE. 



26(3) 



27 (28) 



28 (27) 



29 (30) 



30 (29) 



i 00 



2(1) 

 3(8) 



4(7) 

 5(6) 

 6(5) 



FIG. 1391. The wings of a caddisfly, Hydropsychc. 



Maxillary palpi with fewer than five joints 27 



Maxillary palpi with four joints; ocelli present. Males. 



Family PHRYGANEIDAE. 



Maxillary palpi with two or three joints 29 



Maxillary palpi filiform with cylindric smooth joints; fore tibiae with 



a single spur. Males Family LIMNOPHILIDAE. 



Maxilary palpi hairy or scaly, appressed against and often covering 

 the face; fore tibiae with two spurs. Males. 



Family SERICOSTOMATIDAE. 



KEY TO NORTH AMERICAN AQUATIC BEETLES 

 ADULTS 



Hind tarsi with the antepenultimate segment broadly bilobed, and 

 receiving the rudimentary penultimate segment (which is 

 closely fused with the base of the last segment) in its apical 



notch Family CHRYSOMELIDAE. 



Hind tarsi with the last three segments free and similar in form. . . 3 



Hind legs shorter than the fore; eyes four, two above and two on the 



under surface of the head. . . . Family GYRINIDAE . . 4 



Last abdominal segment rounded posteriorly and smooth below. . . 5 



Wing of the metasternum (w, Fig. 1392) broadly triangular. . Dineutes. 



Wing of the metasternum narrow, elongate, widened only at its extreme 



outer end Gyriwts* 



