AQUATIC INSECTS 



937 



ui (20) 



22 (23) 



23 (22) 



24 (2S) 



25 (24) 



Ocelli wanting 22 



Front tibiffi with three spurs. . . . Family Polycentropidae. 



Spurs of the front tibiae fewer than three. , 24 



Anterior branch of the radial sector in the fore wing forked. 



Family Hydropsychidae. 

 Anterior branch of the radial sector simple. 



Family Psychomyiidae. 



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



26 (3) MaxUlary 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 bUobed, 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) Wingof the metasternumCw, Fig. 1392) broadly triangular. . Dineutes. 



6 (s) Wing of the metasternura narrow, elongate, widened only at its extreme 



outer end. Gyrinm. 



