Cave millipedes of the United States. XVI. Two new species from Oregon Caves National Monument, Oregon (Chordeumatida, Conotylidae and Caseyidae) Author Shear, William A. Author Crawford, Rodney L. text Zootaxa 2019 2019-09-27 4674 5 571 580 journal article 25362 10.11646/zootaxa.4674.5.6 534da4e0-2064-4098-93c2-1f614aef9d2e 1175-5326 3465101 250CE8E7-B7B5-4503-873C-5E79827F6D3C Genus Opiona Chamberlin, 1951 Type species: Opiona columbiana Chamberlin, 1951 . The most recent revision is Gardner & Shelley (1989) ; Shear (2011) adds one more species. Opiona presently includes 14 species and is distributed from central California to the Alexander Archipelago, Alaska ( Gardner & Shelley 1989 , Shelley et al. 2007 ). The single previously described troglomorphic species is Opiona graeningi from caves in the Marble Mountains, Siskiyou Co., California (Shear 2011). Numerous additional surface-dwelling species of Opiona await description and naming. Opiona is best distinguished from other sympatric caseyid genera by the characteristic modification of the third leg, in which the telopodite arises distal to the midpoint of the elongated coxa and has a strongly inflated prefemur ( Figs. 9, 10 ).