A revision of the species group in the millipede genus Chamberlin, 1918 (Diplopoda, Polydesmida, Xystodesmidae).

Although many new species of the millipede genus Chamberlin, 1918 have been known from museum collections for over half a century, a systematic revision has not been undertaken until recently. There are two species groups in the genus: the species group and the species group. In this study, the species group was investigated. Specimens were collected from throughout its distribution in the Appalachian Mountains of the eastern United States and used for a multi-gene molecular phylogeny. The phylogenetic tree recovered and the two species groups as monophyletic, with as its sister group. Seventeen new species were described, bringing the composition of the species group to 24 species, more than tripling its known diversity, and increasing the total number of described species to 78. The genus now has the greatest number of species in the family Xystodesmidae. Museum holdings of were catalogued, and a total of 1,835 records used to produce a distribution map of the species group. Live photographs, illustrations of diagnostic characters, ecological notes, and conservation statuses are given. The species group is restricted to the Appalachian region, unlike the widely-distributed species group (known throughout eastern North America), and has a distinct gap in its distribution in northeastern Tennessee and adjacent northwestern North Carolina. The species group seems to be adapted to mesic microhabitats in middle to high elevation forests in eastern North America. New species are expected to be discovered in the southern Appalachian Mountains.