Mystrium Roger, 1862 Taxonomy. The genus Mystrium is assigned to the tribe Amblyoponini (Bolton 2003). Indo-Australian species were recently revised by Binh and Verhaagh (2007). Morphology. The worker of the Vietnamese species, M. camillae, has the following features: Worker monomorphic; body bearing spatulate hairs; head in full-face view rectangular, with broadly and deeply concave posterior margin, with a short and stout genal spine beside each mandibular insertion; preoccipital carina absent dorsally and laterally; frontal carina and antennal scrobe absent; frontal lobes relatively widely separated by posteromedian portion of clypeus, in full-face view completely concealing antennal sockets, not reaching anterior margin of clypeus; anteromedian portion of clypeus roundly convex anteriad; anterior clypeal margin with a series of 6–8 processes on which a stub-like, very short seta present; mandible elongate, narrowly blade-like, with widened round apex; masticatory margin serrate, with two rows (dorsal and ventral rows) of teeth; antenna 12-segmented, with inconspicuous 4-segmented club; apical segments of antenna never flattened in crosssection; eye absent or present as a single ommatidium; if eye present, it located around midlength of side of head (excluding genal spine); mesosoma in lateral view short and high; promesonotal suture present and flexible; metanotal groove indistinct dorsally; propodeum unarmed; propodeal lobe very low; petiole without distinct anterior peduncle, broadly attached to gaster, in lateral view without a free posterior face; subpetiolar process present; abdominal segment III with a free anterior face below helcium only; girdling constriction between abdominal segment III and IV indistinct; pygidium large, convex across, unarmed laterally and posteriorly; hypopygium armed with a few short spinose setae posteriorly; sting well developed. Differentiation. The worker of Mystrium is somewhat similar to that of Stigmatomma, but in the latter the apex of mandible is pointed, and the body is covered with simple hairs. Vietnamese species (1 sp.). Mystrium camillae Emery, 1889. Au (Cat Tien, Pu Mat, Van Ban), Zry (Cat Tien). Bionomics. Mystrium camillae occurs in well-developed forests but sometimes forest edges and second growth vegetation, and nests under stones and wood fragments. Workers are brown or brick red and dull, bear spatulate hairs, and are often clad in soil. These features make them difficult to detect when their nests are exposed.

Published as part of Eguchi, Katsuyuki, Viet, Bui Tuan & Yamane, Seiki, 2014, Generic Synopsis of the Formicidae of Vietnam (Insecta: Hymenoptera), Part II — Cerapachyinae, Aenictinae, Dorylinae, Leptanillinae, Amblyoponinae, Ponerinae, Ectatomminae and Proceratiinae, pp. 1-46 in Zootaxa 3860 (1) on page 24, DOI: 10.11646/zootaxa.3860.1.1, http://zenodo.org/record/287059