Five Hawaiian species ofParatachysCasey are revised, including four newly described:Paratachys terrylifrom Kauai;P. perkinsifrom Moloka‘i;P. haleakalaefrom Maui; andP. aaafrom Hawai‘i Island. A lectotype is designated for the fifth Hawaiian species currently combined withParatachys,Tachys arcanicolaBlackburn, 1878 of Oahu. HawaiianParatachysspp. known from more than one specimen exhibit some degree of ocular polymorphism, that variation being extreme inP. terryliwhere individuals range in ocular development from macrophthalmic with broadly convex eyes to microphthalmic with small, flat eyes. All HawaiianParatachysspecies comprise individuals with vestigial wings, with the exception ofP. terryli, where a single macropterous, macrophthalmic female complements the other 18 brachypterous specimens. Based on a transformation series of characters from the male aedeagus, the biogeographic history of HawaiianParatachysis consistent with progressive colonization of the Hawaiian Island chain. Three of the species do not appear to represent species of conservation concern, withP. terryliandP. haleakalaeknown from terrestrial deep soil, litter, and streamside microhabitats in montane wet rain forest, and the troglobiticP. aaaoccupying the dark zone of numerous, recently developed lava tube caves within the Mauna Loa and Kilauea volcanic massifs. The conservation status of the other two species is much more dire, withP. arcanicolaof O‘ahu not seen in nature since the early 20thCentury, andP. perkinsiknown only from a single specimen fortuitously collected in 1894 near sea level on Moloka‘i.
