Ranatra Fabricius 1790

1. Posterior margin of metasternum clearly emarginated..........2

– Posterior margin of metasternum convex, or straight or only slightly emarginated................................................................3

2. Vertex with prominent tubercle between eyes; siphon relatively short, ratio of siphon length: body length around 0.2–0.7; fore femur at mid-length of flexor side with one tooth and a carina, or bi-dentate................................................... R. gracilis group

– Vertex with small tubercle or evenly round without tubercle; siphon long, ratio of siphon length: body length around 0.9–1.1; fore femur at mid-length of flexor side with one median tooth, without carina............................................... R. bilobata group

3. Large species, body length at least 37 mm; vertex lower than eye, no tubercle; fore femur at distal 0.3–0.4 of flexor side with one long, narrow tooth; operculum of female clearly surpassing apex of connexivum.................................... R. elongata group

– Smaller species, body length at most 34 mm; vertex higher than eye, with small tubercle or without tubercle; flexor side of fore femur bidentate; operculum of female at most reaching apex of connexivum................................................................4

4. Flexor side of fore femur with one tooth much larger than the other one; siphon long, at least equal to body length.................................................................................. R. malayana group

– Flexor side of fore femur with one tooth slightly larger than the other one; siphon shorter, at most equal to body length....................................................................................................5

5. Fore femur relatively broad, with larger tooth situated at midlength of flexor side ....................................... R. varipes group

– Fore femur slender, with larger tooth clearly situated nearer to distal end of flexor side..........................................................6

6. Eye width clearly less than interocular width............................................................................................... R. filiformis group

– Eye width about subequal to or greater than interocular width................................................................... R. biroi group