AQUATIC INSECTS 937 



21 (20) Ocelli wanting '. 22 



22 (23) Front tibia} 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 Psychomyiidae. 



2; CU2 - 



> 'A ^^2 * 

 Fig. 1391. The wings of a caddisfly, Hydropsyche. 



26 (3) Maxillary palpi with fewer than five joints 27 



27 (28) Maxillary palpi with four joints; ocelli present. Males. 



Family Phryganeidae. 



28 (27) Maxillary palpi with two or three joints 29 



29 (30) Maxillary palpi filiform with cylindric smooth joints; fore tibiae with 



a single spur. Males Family Limnophilidae. 



30 (29) 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 



1 (2) 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. 



2 (i) Hind tarsi with the last three segments free and similar in form. . . 3 



3 (8) Hind legs shorter than the fore; eyes four, two above and two on the 



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



4 (7) Last abdominal segment rounded posteriorly and smooth below. . . 5 



5 (6) Wing of the metasternum {w, Fig. 1392) broadly triangular. . Dineiites. 



6 (5) Wing of the metasternum narrow, elongate, widened only at its extreme 



outer endo Gyrinm* 



