1. Lateral clypeal projections absent; frontal lobes rounded, their largest width posterior to the antennal insertions, from where they curve inwards, not forming a strong constriction; median pronotal projections present; posterior face of mesonotum vertical in side view, with a high posterior projection............................................. ............................ M. urbanus Brandão & Mayhé-Nunes
Lateral clypeal projections present, better seen with head in side view; frontal lobes rounded or subtriangular; median pronotal projections present or absent; posterior face of mesonotum oblique in side view......................2
2. Lateral clypeal projections conspicuous, flat, narrow, curved out and forwards, with rounded apex in side view; frontal lobes subtriangular, the anterior borders rounded, crenulated, and almost as long as posterior borders; median pronotal projections very short or absent ...... ..................... M. cerradensis Brandão & Mayhé-Nunes
Lateral clypeal projections small, triangular in side view; frontal lobes rounded; median pronotal projections present..............................................................................3
3. Posterior vertexal margin weakly notched, between the occipital lobes; mandibles with eight teeth; pair of median pronotal projections laterally flattened, with sharp apex; sagital keel on sternum I of the gaster; integument shagreened, without reticulation; longer and curved erect hairs on body and appendages .............. ..................... M. triangularis Brandâo & Mayhé-Nunes
Posterior vertexal margin strongly notched, between the protrude occipital lobes; mandibles with six teeth; pair of median pronotal projections conical, with blunt apex; sagital keel of sternum I of the gaster inconspicuous; integument finely reticulated; short and curved apressed hairs on body and appendages.......... M. inflatusn. sp.
DISCUSSION
The three species thus far described in Mycetagroicus (M cerradensis - type-species by original designation, M. triangularis and M. urbanus ), and M. inflatusn.sp. , share a peculiar sculpture ( Brandào & Mayhé-Nunes 2001, fig. 4), with all body surfaces covered with regularly spaced, round, minute pits (better seen at relatively high magnifications, up to 70 times), bearing each a deeply set hair, one third the diameter of the pit, sometimes effaced by soil particles; antennal scrobes absent; preocular carinae straight at the eyes level, and evenly curving inwards posteriorly; pronotal shoulders as spine-like triangular projections; mesonotum without conspicuous projections anteriorly, with the posterior dorsal margin oblique to vertical or nearly so, in lateral view; compact petiole, with short to indistinct peduncle; postpetiole always larger and broader than the petiole; disk of tergum 1 of gaster covered by a net of coarse rugulae, more evident anteriorly, sometimes joining similar-sized hair pits.
Mycetagroicus inflatus has the triangular shape of the clypeal minute projections similar to those of M. triangularis (Fig. 4), but can be distinguished from it by the frontal carinae not constricted above the frontal lobes, and by the peculiar relatively shorter pilosity. Furthermore, M. inflatus differs from all other species of the genus by the comparatively more prominent posterior corners of the head; the deeper notch on the vertexal margin; the reticulated integument (better seen in the head, Fig. 1), covered with curved, short hairs; mandibles with six teeth; anterior clypeal margin without median notch; weakly impressed, triangular frontal area; conical and blunt pronotal median and propodeal projections; additional minute pair of projections on mesonotum after the anterior tumuli; deeper impression on the posterior region of postpetiole dorsum; and absence of a keel on the sternum I of gaster.
Mycetagroicus species seems to be quite common, although they are seldom collected. This may result from cryptic habits, enhanced by the peculiar soil-binding sculpture, and also probably as a result of the slow movements these ants show in the field. Mycetagroicus is related to the higher attines ( Brandão & Mayhé-Nunes 2001), that includes Trachymyrmex , Sericomyrmex , Acromyrmex , and Atta , although there is no published phylogenetic proposal for this group.
