Siphunculata and Hemiptera 
277 
g. Ocelli present; beak four-segmented. Ochterid/E and 
Nerthrioe. 
gg. Ocelli wanting; antennae more or less hidden in a groove, 
h. Anterior coxae inserted at or near anterior margin of the 
prostemum; front legs raptorial; beak three-segmented. 
Belostomid^e (withswimming legs), Nepid/e, Naucorid.e. 
i. Metasternum without a median longitudinal keel; antennae 
alw'ays four -segmented. 
j. Beak short, robust, conical; the hairy fleck on the corium 
elongate, large, lying in the middle between the inner 
angle of the membrane and the outer vein parallel to 
the membrane margin; membrane margin S-shaped. 
k. The thick fore femur with a relatively deep longitudinal 
furrow to receive the tibia. Several American 
species (fig. 19f.). . .Belostoma ( = Lethocerus Mayer) 
kk. The less thickened fore femur without such a furrow 
.B. griseus. Benacus Stal. 
jj. Beak slender, cylindrical; the hairy spot on the corium 
rounded lying next to the inner angle of the membrane, 
k. Membrane large, furrow of the embolium broadened. 
Z. aurantiacum, fluminea, etc. Zaitha 
kk. Membrane very short; furrow of embolium not 
broadened. Western genus. Pedinocoris 
ii. Metasternum with a long median longitudinal keel. South¬ 
western forms. A bedus ovatus and Deniostoma dilatato 
hh. Anterior coxae inserted at the posterior margin of the 
prosternum; legs natatorial. Back swimmers (fig. 19 b.) 
. NOTONECTIDjE 
i. Apices of the hemelytra entire; the three pairs of legs 
similar in shape; beak three-segmented; abdomen not 
keeled or hairy. Plea Leach 
ii. Apices of hemelytra notched; legs dissimilar; beak four- 
segmented; abdomen keeled and hairy, 
j. Hemelytra usually much longer than the abdomen; 
fourth segment of the antenna longer than the third 
segment; hind tarsi with claws . Bueno Kirk. 
jj. Hemelytra but little longer than the abdomen; fourth 
segment of the antenna shorter than the third seg¬ 
ment; hind tarsi without claws (fig. 19b). . Notonecta L. 
ff. Antennae longer than the head; or if shorter, then the eyes and 
ocelli absent. 
g. Eyes, ocelli, and scutellum wanting; beak three-segmented; 
head short; hemelytra always short; membrane wanting. 
Insects parasitic on bats. Polyctenid.e 
gg. Eyes present. 
h. First tw r o antennal segments very short, last two long, pilose, 
third thickened at the base; ocelli present, veins of the 
hemelytra forming cells. Dipsocorid.e ( = Ceratocombi- 
d.e) including Schizopterid.e. 
