Contribution to the knowledge of the subgenus Tenuibaetis Kang & Yang 1994 (Ephemeroptera, Baetidae, Baetis s. l.).

The taxon Tenuibaetis Kang & Yang (in Kang, Chang & Yang) 1994 is accepted here as a subgenus of the genus Baetis Leach 1815, but not as a genus. In connection with this, new combinations are established: Baetis (Tenuibaetis) parvipterus (Fujitani et al. 2011) comb. n., Baetis (Tenuibaetis) fujitanii (Kaltenbach & Gattolliat 2019) comb. n., Baetis (Tenuibaetis) himani (Kubendran et al. in Kubendran et al. 2022) comb. n., Baetis (Tenuibaetis) kangi (Kubendran et al. in Kubendran et al. 2022) comb. n. and Baetis (Tenuibaetis) panhai (Suttinun et al. 2022) comb. n. Based on reared material, imagines of both sexes and larvae of Baetis (Tenuibaetis) ursinus Kazlauskas 1963, Baetis (Tenuibaetis) hissaricus Novikova 1991, Baetis (Tenuibaetis) frequentus Müller-Liebenau & Hubbard 1985 (= Indobaetis michaelohubbardi Selva-kumar et al. 2012, syn. n.) and B. (T.) fujitanii are redescribed. B. (T.) panhai is redescribed based on subimago reared from larva. Two new species from Southern India, Baetis (Tenuibaetis) kaltenbachi sp. n. and Baetis (Tenuibaetis) bialatus sp. n. are described based on imagines reared from larvae. A new species from Thailand, Baetis (Tenuibaetis) octomaculatus sp. n. is described based on imagines reared from larvae.