Key to males of Mecistogaster recorded in the Brazilian Atlantic Forest

1. Costal margin at level of pseudostigma of HW not projected anteriorly; cerci in lateral view straight........... M. linearis

1’. Costal margin at level of pseudostigma of HW abruptly projected anteriorly (Fig. 12); apex of cerci in lateral view bent ventrally (Fig. 28)........................................................................................ 2

2. Anterior hamule with alula (Fig. 17)...................................................................... 3

2’. Anterior hamule without alula (Fig. 18).................................................................... 4

3. Mesepimeron totally reddish-brown (Fig. 9); penis segment 2 in ectal view with one lateral elevation, in lateral view with contour foot-shaped (Figs 23, 24).................................................................... M. amalia

3’. Mesepimeron with reddish-brown area restricted to lower 1/5 of sclerite (Fig. 8); penis segment 2 in ectal view with two lateral elevations, in lateral view with contour not foot-shaped (Figs 25, 26)........................... M. nordestina sp. nov.

4. Mesepimeron with reddish-brown area restricted to lower 1/5 of sclerite (Fig. 8); contour of penis segment 2 in lateral view with dorsal and ventral margin straight (Fig. 22), apex of inner fold projected ventroapically as a tubercle (Fig. 22)........................................................................................... M. kesselringi sp. nov.

4’. Mesepimeron totally reddish-brown (Fig. 9); contour of penis segment 2 in lateral view with dorsal margin undulated and ventral margin with a semicircular elevation at midlength (Fig. 20), apex of inner fold hardly visible, not projected ventroapically (Fig. 20).............................................................................. M. mielkei sp. nov.