Key to the species of Hydrometra from India

1. Abdominal tergum 8 rectangluar; sternites 7 or both 7 and 8 with setal tuft, setal patch, protuberance, thorn-like structure, dispersed long hairs (males)................................................................................ 2

- Abdominal tergum 8 sub-triangluar; sternites 7 or both 7 and 8 without any specialized characters like setal tuft, setal patch, protuberance, thorn-like structure or dispersed long hairs (females).............................................. 6

2. Males. Anteclypeus broad with anterior margin slightly concave medially, maxillary plate extending in front of anteclypeus (Fig. 2D), body dark brown to black colour. 7th sternite with a pair of setal patches near posterior region and 8th abdominal sternite with a pair of setal tuft near anterior region (Figs. 4C, 5C)............................. H. cherukolensis sp. nov.

- Anteclypeus conical, body yellow to dark brown colour....................................................... 3

3. Seventh abdominal sternite with a pair of thorn-like processes, caudal process short (Fig. 6 C-E)....... H. okinawana Drake

- Seventh abdominal sternite without thorn-like processes, but with dispersed setae or patch of setae; caudal process long.... 4

4. Seventh abdominal sternite not swollen but with transverse depression medially; sternites 6 and 7 with dispersed long setae, pronounced in segment 7 (Fig. 4E, 5E)...................................................... H. greeni Kirkaldy

- Seventh abdominal sternite swollen, with a pair of setal patches (Figs. 4A,G; 5A,G)................................. 5

5. Lateral margin of setal patch on seventh abdominal sternite lined with long curved hairs; posterior part of sixth sternite and the whole seventh abdominal sternite with dispersed setae (Figs. 4G, 5G)......................... H. nicobarensis sp. nov.

- Sixth and seventh abdominal sternites without dispersed setae, seventh abdominal sternite with a pair of small round patch of short setae and a row of little longer setae adjacent to setal patch continued postero-laterally (Figs. 4A, 5A)......................................................................................... H. butleri Hungerford and Evans

6. Females. Anteclypeus broad with anterior margin concave medially; posterior region of sternite 7 triangularly produced, partly covering gonocoxae medially, without any characteristic hairs; caudal process is straight caudad, (Figs. 3D, 4D, 5D)........................................................................................ H. cherukolensis sp. nov.

- Anteclypeus conical, posterior region of sternite 7 clothed with dense short procumbent hairs; caudal process straight caudad, ventrocaudad, slightly dorsocaudad....................................................................... 7

7. Subapex of sternite 7 with a shallow, half-circle depression; caudal process is slightly dorsocaudad, anterior margin in lateral view convexed (Figs. 4H, 5H)........................................................ H. nicobarensis sp. nov.

- Subapex of sternite 7 without any depression; caudal process is straight caudad, ventrocaudad......................... 8

8. Caudal process is ventrocaudad, posterior region of tergite 7 raised, margin bordered with short hairs (Figs. 3F, 4F, 5F)........................................................................................... H. greeni Kirkaldy

- Caudal process is straight caudad......................................................................... 9

9. Caudal process stout, with fringe of hairs (Figs. 3B, 4B, 5B)......................... H. butleri Hungerford and Evans

- Caudal process slender, without characteristic fringe of hairs................................... H. okinawana Drake