periodicus, Cynolebias Costa [W. J. E. M.] 1999:299, Figs. 1-2 [Ichthyological Exploration of Freshwaters v. 10 (no. 4); ref. 24229] Temporary flood-plains of the rio Santa Maria, rio Ibicuí drainage, rio Uruguai basin, road BR-293, 4 kilometers west from Dom Pedrito, Estado do Rio Grande do Sul, Brazil. Holotype: MCP 20819. Paratypes: MCP 20820 (5); MZUSP uncat. (4); UMMZ 234761 (4); UFRJ 4671 (12), 4672 (6, c&s). •Valid as Austrolebias periodicus (Costa 1999) -- (Lazara 2001:63 [ref. 25711], Costa 2002:917 [ref. 26505], Costa in Reis et al. 2003:528 [ref. 27061], Costa 2006:83 [ref. 28708], Litz & Koerber 2014:30 [ref. 33622], Bertaco et al. 2016:424 [ref. 34561], Nión et al. 2016:43 [ref. 35565], Volcan et al. 2017:151 [ref. 35644], Loureiro et al. 2018:11 [ref. 36240], Loureiro et al. 2023:166 [ref. 40506]). •Valid as Matilebias periodicus (Costa 1999) -- (Alonso et al. 2023:9 [ref. 40292], Koerber et al. 2023:11 [ref. 40355]). Current status: Valid as Matilebias periodicus (Costa 1999). Rivulidae: Cynolebiinae. Distribution: South America: Uruguay River basin (Argentina, Brazil and Uruguay). Habitat: freshwater.