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 Galerucetta. 



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 (u) 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 Peltodytes. 



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



Family DYTISCTDAE. 



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. 



1 8 (17) Body little depressed; cerci wanting; gills rarely present (and then 



lateral in position, Berosus). . . Family HYDROPHILIDAE. 



KEY TO NORTH AMERICAN AQUATIC DIPTEROUS LARVAE 



1 (65) 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 (58) Mandibles opposed to each other, or inclined obliquely 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 j 



