LIBRARY

270
COLLEGE ENTOMOLOGY
3. Base of head overlapping front margin of pronotum. Rostrum very
short, scarcely distinguished from the broad apex of head. Front
tarsi one-segmented, spatulate, and fringed with strong bristles.
(Water Boatmen.) . CORIXIDlE
Base of head inserted in pronotum. Rostrum cylindrical or cone-shaped
and distinctly segmented. Front tarsi not as above. 4
4. Abdomen with a pair of short strap-like or long slender posterior appendages
. 5
Abdomen without such posterior appendages. 6
5. Posterior: abdominal appendages long and slender, forming a respiratory
siphon. Hind legs cylindrical, formed for walking. Hind coxre
globular. (Water Scorpions.) . NEPIDlE
Posterior abdominal appendages short, flat, retractile, sometimes concealed
heneath the tips of hemelytra. Hind legs flattened, fringed,
fitted for swimming, the hind coxre hinged. (Giant Water Bugs.)
BELOSTOMATIDlE
6. Body broad, oval. and flattened. Front femora tremendously enlarged
and grooved along inner edge where they oppose the prehensile,
curbed tibire. (Water Creepers.) . . NAUCORIDlE
Body strongly convex above, either elongate and large, over 5 mm .. or
more rounded and small, less than 3 mm. Front femora not greatly
enlarged . 7
7. Form elongate. Size large, 5 mm. or more. Hind tibire and tarsi densely
clothed with swimming hairs. Abdomen with a ventral trough or
concavity in which is a median carinate ridge. Antennre four-segmented.
(Back Swimmers.) . NOTONECTIDlE
Form suboval. Size small, less than 3 mm. Hind tibire and tarsi
scarcely, if at all, clothed with swimming hairs. Abdomen neither
deeply ::oncave nor carinate beneath . PLEIDlE
8. Antennre exposed. Eyes not strongly protuberant. Front legs similar
to middle pair, fitted for running. (Velvety Shore Bugs.) OCHTERIDlE
Antennre concealed in grooves beneath the strongly protuberant eyes.
Front legs raptorial, the femora very broad and grooved along their
inner edges nearest the curved tibire. (Toad Bugs.) GELASTOCORIDlE
9. Claws of at least the front tarsi inserted before the apex, the tip of the
last tarsal segment cleft. Superfamily GERROIDEA . 10
Claws all located at the tips of the tarsi, the tarsal apices entire. 11
10. Hind femora very long, greatly exceeding apex of abdomen. (Water
Striders.) . . GERRIDlE
Hind femora scarcely, if at all, surpassing tip of abdomen. (Smaller
Water Striders.) . . VELllDlE
"1. Head as long as the entire thorax. (Marsh Treaders.) HYDROMETRIDlE
Head shorter, not exceeding the combined length of pronotum and
scutellum . 12
1':. Body clothed with short, velvety pile, at Jeast ventrally. Both clavus
and membrane membranous and devoid of veins. Small (less than
4 mm.) semiaquatic bugs with legs fitted for running or walldng on
the water . . . . .. 13
Body not clothed with fine, hydrofuge pile. Terrestrial • 14
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