Key for identification of South American species of Crossopalpus Bigot ( Diptera, Hybotidae, Tachydromiinae)

1 Scutum not densely bristled, with only few acrostichal (acr) and dorsocentral (dc) bristles (Figs 24, 26, 30). Fore and mid tibiae yellow (Figs 23, 25, 29)............................................................................... 2

- Scutum densely bristled, bearing several rows of acr and dc bristles (Figs 16, 18, 28). At least fore or mid tibiae darkened (Figs 10, 16, 17, 27), reddish-yellow to brown................................................................... 4

2 Frons and vertex with patch of white tomentum (Fig. 24). Antennae black, postpedicel concolorous with preceding segments (Figs 23, 24). Femora concolorous, yellow (Figs 23–24). Shorter species, about 1 mm ............... C. albivertex sp. nov.

- Frons and vertex without patch of white tomentum (Figs 26, 30). Antennae dark brown to yellow, postpedicel lighter in color than preceding segments (Figs 26, 29, 30). Hind femur darker than fore and mid femora (Figs 25, 29). Longer species, about 2 mm ............................................................................................... 3

3 Palpus (Fig. 29) and abdomen yellow (Figs 29, 30). Hind tibia darkened (Fig. 29). Wing milky, with no infuscation, second costal section 2/3 length of third costal section (Fig. 35).................................... C. xanthogaster sp. nov.

- Palpus dark brown (Fig. 25), abdomen pale brown (Figs 25, 26). Tibiae concolorous, yellow (Fig. 25). Wing slightly brown infuscate near base, second costal section about as long as third costal section (Fig. 32)............... C. aliceae sp. nov.

4 Palpus yellow (Figs 10, 17). Fore and mid femora with brown to reddish-brown extensive markings, hind femur black (Figs 10, 16, 17). Wing hyaline, lacking infuscation, venation pale brown to brown (Figs 16, 17)........................... 5

- Palpus somewhat darkened, brownish-yellow. Fore and mid femora brownish-yellow, hind femur brownish-yellow with brown infuscation on apical 2/3 (Figs 27, 28). Wing brown infuscate, venation dark brown to black (Fig. 34)... C. goliathus sp. nov.

5 Head lacking tomentum on upper 1/2 of postocular area. Fore tibia yellow (Fig. 10). Hind femur slender (Fig. 10), bearing 2 subapical anteroventral setae. Vein R 4+5 only slightly arched, M 1 slightly bowed, initially divergent from each other and convergent near apex (Fig. 33)............................................................ C. armipes (Bezzi, 1909)

- Head tomentose on upper 1/2 of postocular area (Fig. 16). Fore tibia brownish-yellow (Fig. 17). Hind femur strongly swollen (Figs 16, 17), bearing 1 subapical anteroventral strong seta. Both veins R 4+5 and M 1 strongly arched, parallel throughout (Figs 16, 17).................................................................... C. pennescens (Melander, 1918)