Key to species of Bidessus on Madagascar

1. Elytral stria long, approximately half the length of elytron (Figs 1A, 2C) ...................................... 2

– Elytral stria short, distinctly shorter than half the length of elytron (Figs 1 B–D, 2A–B) ................ 3

2. Elytral stria straight (Fig. 1A); female ventrite with a deep, longitudinal furrow; female elytron posteriorly with a distinct, lateral extension (Fig. 1A) ...... B. apicidens Biström & Sanfilippo, 1986

– Elytral stria sinuate (Fig. 2C); female ventrite simple, no longitudinal furrow; female elytron posteriorly smooth, lacks extension .................................................. B. longistriga Régimbart, 1895

3. Small species (max. length 1.5 mm); elytra with distinct, longitudinal, pale markings (Fig. 2B) ..... .................................................................................................................. B. perexiguus Kolbe, 1883

– Larger species (length 1.5–2.0 mm); elytra predominantly dark, sometimes with minor, vague, pale markings (Figs 1 B–D, 2A) ............................................................................................................... 4

4. Frontal transverse depression of head transformed to four minor, slightly vague, tubercles (Fig. 1B) ................................................................................................. B. cf. ceratus Guignot, 1941

– Frontal transverse depression of head not transformed to small tubercles (depression laterally distinct, medially vague) ................................................................................................................... 5

5. Head and pronotum mainly pale, testaceous (Fig. 1D) ................... B. cf. nero Gschwendtner, 1933

– Head distinctly darker than pronotum (Figs 1C, 2A) ....................................................................... 6

6. Elytral stria longer (approximately ⅓ of elytron length); body shape broad (Fig. 1C); pronotum extensively pale (dark markings reduced to narrow areas close to frontal and posterior edges) (Fig. 1C); antenna pale (Fig. 1C) .................................................................... B. anjozorobe sp. nov.

– Elytral stria short (less than ⅓ of elytron length); body shape slender (Fig. 2A); pronotum extensively dark (pale markings reduced to quite narrow medial area, often divided into two separate spots) (Fig. 2A); antenna segments 4–11 dark (Fig. 2A) ................................. B. nesioticus Guignot, 1956