Key to the species of Microcharacidium

1. Circumpeduncular scales 14; total dorsal-fin rays 12; 7–11 lateral line perforated scales........................ M. gnomus

1 '. Circumpeduncular scales 12 or 10; total dorsal-fin rays 11 or fewer; usually fewer than 7 perforated lateral line scales...... 2

2. Circumpeduncular scales 12; 7 dark bars................................................................ M. bombioides

2 '. Circumpeduncular scales 10; 8 or more dark bars; precaudal vertebrae 16–17......................................... 3

3. Conical teeth; 1 suborbital bar; 20–25 scales in lateral line longitudinal series............................. M. weitzmani

3 '. Tricuspid teeth; 2 suborbital bars; 11–12 ectopterygoid teeth; 27–32 scales in lateral line longitudinal series..... M. eleotrioides