AQUATIC INSECTS 943 



Larvae 



1 (4) Herbivorous larvae with short, broad inconspicuous mandibles. 



Family Chrysomelidae . 2 



2 (3) Feeding exposed on the floating leaves of water lilies, etc.; elongate 



brownish larvae of sluggish habits Galerucella. 



3 (2) Short arcuate grublike larvae, white and translucent, feeding on the 



submerged roots of aquatic plants Donacia. 



4 (i) Carnivorous larvae, with prominent mandibles. 5 



5 (12) Mandibles sickle-shaped without internal teeth, but with an internal 



groove or perforation extending almost from base to apex. 6 



6 (7) End of the abdomen with two pairs of strong claws, and the middle 



segments bearing single pairs of long lateral filaments. 



Family Gyrinidae. 



7 (6) No claws at end of abdomen 8 



8 (11) Eyes in groups of five; one claw on each tarsus. 



Family Haliplidae . . 9 



9 (10) Body nearly smooth, ending in a long tail. . . . Haliplus. 



10 (9) Body bearing numerous very long and conspicuous bristlelike fila- 



ments; no tail Pellodytes. 



11 (8) Eyes in groups of six; two claws on each tarsus. 



Family DYTiscroAE. 

 12(5) Mandibles toothed internally, at base or in the middle 13 



13 (14) Tarsi with two claws Amphizoa. 



14 (13) A single claw on each tarsus 15 



15 (16) Antennae as long as or longer than the thorax. 



Family Dascyllidae. 



16 (15) Antennae shorter than the thorax 17 



17 (18) Larvae depressed; end of the abdomen with short cerci; gills, when 



present, ventral in position. . . , . . Family Parnidae. 



18 (17) Body little depressed; cerci wanting; gills rarely present (and then 



lateral in position, ^ewiMi) . . . Family Hydrophilidae. 



KEY TO NORTH AMERICAN AQUATIC DIPTEROUS LARVAE 



1 (6s) Head chitinous, free, or retracted within the front of the prothorax. 



Pupa usually free; when concealed in the old larval skin, 

 that skin splits on emergence of the imago in a longitudinal 

 I- or T-shaped cleft. . . . Suborder Orthorrhapha . . 2 



2 (s8) Mandibles opposed to each other, or incHned obKquely downward 



and opposed to a strongly chitinized labial border. 



Nematocera . . 3 



3 (4) Body strongly depressed, and with a row of six ventral suckers for 



attachment to the rock bed of rapid streams. 



Family Blepharoceridae 



4 (3) Body cylindric, and usually lacking ventral suckers; when ventral 



suckers are developed they are more than six 5 



