[here designated]. Worker: CASENT0102123, MYANMAR, Bhamo, iv.1886, Fea leg. [MSNG: examined].

The lectotype for Mystrium camillae is designated here. We confirm that five workers collected from vi.1885 to iv.1886 are part of the syntype series: two workers in MSNG [CASENT0102123, CASENT0102124]; one worker in MNHN [CASENT0101450]; and two workers in MHNG [CASENT0101809, CASENT0101784]. Although Emery (1889) described a queen in his original description, we could not find the syntype queen. According to the original description (Emery 1889), the queen is dealate, and was not collected from the same colony as any of the syntype workers.

According to the revision of Mystrium in the Indo-Australian region (Bihn and Verhaagh 2007), Mystrium camillae is widely distributed in the Indomalaya, and Australian regions: from Australia to Brunei, China, India, Indonesia, Malaysia, Myanmar, Papua New Guinea, the Philippines and Singapore. We find that specimens currently determined as Mystrium camillae display remarkable morphological variation, some of which appears not to be intra-specific but rather due to differences among species. For example, we found a small-sized queen with vestigial wings in Indonesian material (CASENT0009854), workers with longer setae on the anteromedial portion of the clypeus in specimens from New Guinea, a large queen with simple setae on the pronotal dorsum in specimens from China (CASENT0275389), and a strange yellow male from Australia (CASENT0172083).

We have found that clarifying species boundaries in the genus Mystrium is much more complicated than would be expected from previous studies. The differences among some sibling species similar to Mystrium camillae could be recognizable only in a particular sex, caste, or phenotype, as in the case of Mystrium camillae and Mystrium barrybressleri. A reexamination of the species boundaries of Mystrium camillae based on a detailed comparative study using comprehensive colony samples from each local region will be necessary.