Shear, W. A. Cave Millipeds of the United States. XI. Opiona Graeningi, n. sp., a Troglomorphic Caseyid Milliped from Siskiyou County, California, With Comments on the Genus Opiona Chamberlin 1951 (Diplopoda, Chordeumatida, Caseyidae). Zootaxa 2011, 3114, 50–56.