Key to species of the M. amazonensis species-group (male and female specimens)

1 Thorax yellow. Male terminalia yellow. Female terminalia white............................ M. albicaudatus sp. nov.

- Thorax predominantly black. Male and female terminalia black................................................ 2

2 Mesopleuron yellow adjacent to all coxae.................................................. M. acreanus sp. nov.

- Mesopleuron entirely black............................................................................. 3

3 Prosternum and part of propleuron yellow............................................... M. trombetensis sp. nov.

- Prosternum and propleuron entirely black................................................................. 4

4 Male terminalia with posterior cercus curved inwards (Fig. 47). Female hind tibia without pinnate setae. Female fore coxa black, mid and hind coxae yellow. Female and sometimes male hind femur black and yellow banded.... M. xavieri sp. nov.

- Male terminalia with posterior cercus curved upwards (Figs 20, 31). Female hind tibia with pinnate setae along dorsal margin and basal third ventrally (Figs 24, 34). Female fore, mid and hind coxae yellow. Female and male hind femur black at apex only............................................................................................... 5

5 Male terminalia with hypandrium bearing acute protuberance posteriorly (Fig. 22). Female sternite 8 around 2.2 times longer than wider (Fig. 27)................................................................ M. amazonensis sp. nov.

- Male terminalia with hypandrium lacking acute protuberance posteriorly (Fig. 33). Female sternite 8 around 3 times longer than wider (Fig. 37)................................................................... M. paraiba sp. nov.