Key to the trans-Andean and Central-American species of Imparfinis

1. Maxillary barbels reaching to or exceeding pelvic-fin origin ....................................................................................... 2

1’. Maxillary barbels not reaching pelvic-fin origin ................ 4

2. First ray of dorsal fin longer than second ray; maxillary barbel surpassing pelvic-fin base ....................................... 3

2’. First ray of dorsal fin shorter than second ray; maxillary barbel reaching pelvic-fin origin (reaching anal-fin origin in some juvenile specimens) ......................... I. timana (Figs. 1, 5g; río Guarapas, upper río Magdalena basin)

3. First ray of dorsal fin projecting beyond fin margin as a long filament (length of first dorsal-fin ray: 29.2-33.1% in SL); pectoral fin surpassing pelvic-fin origin; lower caudal-fin lobe pointed, with lower branch of lowermost branched ray longer than upper branch, and extended as a filament ............... ............................................ I. nemacheir (Figs. 5 b-d; río Atrato, río Magdalena and lago de Maracaibo basins)

3’. First ray of dorsal fin not projected as a long filament (length of first dorsal-fin ray: 19.1-23.2% in SL); pectoral fin not reaching pelvic-fin origin; lower caudal-fin lobe rounded in specimens longer than 30 mm SL, with both branches of lowermost branched ray approximately equal in length .................................................................. I. usmai (Figs. 3, 4, 5a; río Patía, río Cauca and río Magdalena basins)

4. Maxillary barbel extending to half the length of pectoral fin, adipose-fin length: 17.2-18.6% in SL ................. I. lineatus (Fig. 5h; streams in Pacific versant of northern Costa Rica)

4’. Maxillary barbel extending to end of pectoral fin, adiposefin length:21.1-22.9% in SL .................................... I. spurrellii (Fig. 5e; río San Juan basin)