The True Bugs 



Antennae at least as long as the head, usually free, rarely (in 

 Phymatidiie) lying in a groove along the side of the pro- 

 notum 4 



I — Hind tarsi without claws 2 



Hind tarsi with two claws 3 



2 — Fore tarsi flattened, ciliated on edge, without claws; head 



overlapping prothorax Corixida: 



Fore tarsi not flattened, with two claws; head inserted into 

 prothorax Notonectidce 



} — Abdomen with two grooved filaments at tip, forming to- 

 gether a respiratory tube which is not retractile, Nepidce 

 Abdomen without respiratory tube. 



Legs formed for swimming; tip of abdomen with two 



retractile strap-like appendages Belostomatidx 



Legs formed for walking; abdomen with no such ap- 

 pendages. 



Ocelli absent Naucoridce 



Ocelli present Galgulidce 



4 — Antennae with their bases visible from above, usually four- 

 jointed; rarely five-jointed, (not counting the minute in- 

 termediate segments sometimes present.) 



Scutellum less than half as long as abdomen 5 



Antenni^ with their bases not visible from above, five-jointed. 

 Scutellum more than half as long as abdomen 14 



5 — Beak three-jointed, sometimes four-jointed, with basal seg- 

 ment very short and inconspicuous 6 



Beak four-jointed, with plain basal segment 10 



6 — Body very slender; head as long as thorax . . Hydrometridce 

 Body of various shapes, but when slender, head shorter than 

 thorax. 



Last segment of tarsi more or less bifid, with the claws in- 

 serted before the tip Hydrobatidce 



Last segment of tarsi entire, claws at tip. 



Hemelytra usually well developed and without cuneus. 



When Hemelytra is absent ocelli are present 7 



Hemelytra with cuneus Anthocorid(B 



Hemelytra rudimentary, ocelli absent Cimicidce 



7 — Hind tarsi with three segments 8 



Hind tarsi with two segments 9 



271 



