New Pacific material of the cosmopolitan genus Agathotanais Hansen, 1913 has made a generic revision possible. Newly discovered character states for the antenna have made it necessary to modify the generic diagnosis. Three new species A. manganicus and A. ahyongi from the central Pacific and A. spinipoda from the continental shelf and slope off southeastern Australiaare described, they increase the number of species in the genus to eight. A key to the females of Agathotanais species is provided. Sexual dimorphism is generally restricted to the presence of pleopods in the male. The characters defining Agathotanais are considered apomorphic within the Tanaidomorpha. The distribution pattern of Agathotanais is discussed.