Key to species of Neoplecostomus

1 Dorsal-fin spinelet absent or weakly developed, usually narrower than dorsal-fin spine...........................2

- Dorsal-fin spinelet present and always wider than dorsal-fin spine............................................................3

2 Three plates in ventral head region, just ahead gill openings; dentary teeth followed by two rows of large and transversally flattened papillae ......................................................................................... N. ribeirensis

- One large plate in ventral head region, just ahead gill openings; dentary teeth followed by three irregular rows of large and transversally flattened papillae ............................................................. N. franciscoensis

3 Adipose fin absent or poorly developed ................................................................................ N. paranensis

- Adipose fin well developed.........................................................................................................................4

4 Mature males with enlarged odontodes on distinct swollen skin, along lateral margins of snout...............5

- Mature males without enlarged odontodes on distinct swollen skin along lateral margins of snout...........6

5 Mature males with enlarged odontodes on distinct swollen skin along a ridge in front of eye..................... ............................................................................................................................................ N. selenae n. sp.

- Mature males neither with enlarged odontodes or distinct swollen skin along a ridge in front of eye ......... ................................................................................................................................................ N. yapo n. sp.

6 Plates in lateral line 34 to 43; plates between adipose and caudal fin 10 to 13........................ N. granosus

- Plates in lateral line 27 to 33; plates between adipose and caudal fin 4 to 9...............................................7

7 Cleithral width 24.9 to 27.6% of SL; orbital diameter 12.2 to 13.0% of HL ................... N. corumba n. sp.

- Cleithral width 17.0 to 23.0% of SL; orbital diameter 6.0 to 11.0% of HL................................................8

8 Premaxilary teeth 19 to 38 and dentary teeth 15 to 35 ................................................. N. espiritosantensis

- Premaxilary teeth 9 to 17 and dentary teeth 5 to 12....................................................................................9

9 Head length 26.2 to 26.8% of SL; cleithral width 25.3 to 25.4% of SL................................. N. variipictus

- Head length 29.0 to 32.0% of SL; cleithral width 19.0 to 23.0% of SL..................................... N. microps