Key to the species of the gigas group

1. Head without transverse carina, horn or tubercle along frontoclypeal suture. Cerrado-Atlantic Forest transition in São Paulo state (Brazil) ............................. Canthidium (Neocanthidium) ayri sp. nov.

– Head with a transverse carina, conical horn or tubercle along the frontoclypeal suture .................. 2

2. Head with conical horn. Hypomeron with incomplete hypomeral carina (Fig. 1B). Brazilian Cerrado and neighbouring open area ............... Canthidium (Neocanthidium) kelleri (Martínez et al., 1964)

– Head with either short or long transverse carina, lacking a horn. Hypomeron with complete hypomeral carina (Fig. 1A). Known from forested/shaded habitats ................................................................... 3

3. Head with a long transverse frontoclypeal carina, length greater than one half interocular width. Pronotum anteriorly with a shallow excavation near centre (absent in small specimens and smaller in females than in males); bordered anteriorly by a transverse bilobed carina (reduced to a pair of lobes in smaller individuals). Amazonia ........................................................................................... 4

– Head with a short transverse frontoclypeal carina, length less than one-third of interocular width. Pronotum convex anteriorly, without evident lobes or excavations. Chaco, Cerrado and Atlantic Forest ................................................................................................................................................ 5

4. Frontoclypeal carina with length less than three-fourths of interocular width. Pronotum with anterior carina and lobes not evident, positioned just behind anterior border and separated from border by distance less than the border width; anterior region of disc punctate, posterior region with indefinite punctation (Fig. 1D). French Guiana ............................ Canthidium (Neocanthidium) feeri sp. nov.

– Frontoclypeal carina with length greater than four-fifths of interocular width. Pronotum with both anterior carina and two lobes sharply evident, separated from border by a distance equal or greater than the latter’s width; disc with surface completely punctate (Fig. 1C). Amazon rainforest south of the Amazon River in Brazil and Peru ........................ Canthidium (Neocanthidium) stofeli sp. nov.

5. Parameres, in dorsal view, with strong median angulation and concave apical excavation (Fig. 2C); in lateral view, with dorsomedial angulation of 120° (Fig. 2D). Brazilian Atlantic Forest, including intrusions into Cerrado ................................... Canthidium (Neocanthidium) gigas Balthasar, 1939

– Parameres, in dorsal view, with feeble median angulation and shallow apical excavation (Fig. 3C); in lateral view, with dorsomedial angulation of 160° (Fig. 3B). Chaco and western Cerrado in Brazil, Bolivia, Paraguay and Argentina ........................................................................................................ .................................................. Canthidium (Neocanthidium) bokermanni (Martínez et al., 1964)