(syn. Oxyura Ϯ Blue-billed Duck O. australis) L. pervicax, pervicacis firm, stiff < per- very; vincere to overcome; cauda tail; "The genotype of Oxyura Bonaparte, 1828, and of Erismatura, 1832, of the same author, is Anas jamaicensis Gmelin, which has twenty tail feathers. In The Birds of Australia, vol. 4, p. 136, February 17, 1915, I fully diagnosed the genus as applied to the Australian bird described by Gould in 1837 as Oxyura australis, which has sixteen tail feathers, and therefore requires a genus name on account of this structural difference. Pervicauda genus new, for Oxyura australis Gould, with sixteen tail feathers, thus differing from A. jamaicensis, which has twenty tail feathers" (Mathews 1945).