Shear, William 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 3114, no. 1 (November 30, 2011): 50–56. Accessed May 3, 2025. https://www.mapress.com/zt/article/view/zootaxa.3114.1.5.