Key to species of Onconida Baba & de Saint Laurent, 1996

1. Carapace with low gastric process, height less than one-fifth that of carapace (measured laterally between dorsal surface and linea anomurica)............................................... Onconida modica Baba & de Saint Laurent, 1996

- Carapace with high gastric process, height more than one-fourth that of carapace (measured laterally between dorsal surface and linea anomurica).................................................................................. 2

2. Abdominal somite 4 unarmed...................................... Onconida tropis Baba & de Saint Laurent, 1996

- Abdominal somite 4 with pair of submedian spines........................................................... 3

3. Dactylus of ambulatory legs with 3 or 4 flexor movable spines.................................................. 4

- Dactylus of ambulatory legs with 7 or 8 flexor movable spines.................................................. 5

4. Carapace gastric process anteriorly produced, very high, height more than one-third carapace height (measured laterally between dorsal surface and linea anomurica). Antennal article 2 narrow, width about half the length (excluding spines)................................................................... Onconida alaini Baba & de Saint Laurent, 1996

- Carapace gastric process not anteriorly produced, moderately high, height less than one-third that of carapace (measured laterally between dorsal surface and linea anomurica). Antennal article 2 broad, width about two-thirds the length (excluding spines)............................................................................ Onconida ariel sp. nov.

5. Rostral spine with two longitudinal rows of successive oblique scale-like ridges dorsally. Distolateral spine of antennal article 2 small, not overreaching midlength of article 3...................... Onconida gemini Baba & de Saint Laurent, 1996

- Rostral spine with two uninterrupted longitudinal ridges dorsally. Distolateral spine of antennal article 2 strong, reaching end of article 3................................................. .. Onconida prostrata Baba & de Saint Laurent, 1996