orthus, Hemigrammus Durbin [M. L.] 1909:61 [Annals of the Carnegie Museum v. 6 (no. 1); ref. 1166] Tukeit, Guyana. Holotype: FMNH 53052 [ex CM 1477]. Paratypes: (43) BMNH 1911.10.31.394 (1); CAS 44465 [ex IU 11921, not 11912] (5), 44466 [ex IU 11922] (6); FMNH 7348 (1), 53053-56 (6, 5, 1, 6); MCZ 29978 [ex CM/IU] (1); CAS-SU 21781 (1); USNM 66190 [ex CM] (1); ZMA 100977 (1). Type catalog: Henn 1928:65 [ref. 12305], Böhlke 1953:24 [ref. 12291], Nijssen et al. 1982:19 [ref. 19236], Ibarra & Stewart 1987:45 [ref. 12367], Vari & Howe 1991:25 [ref. 19022]. •Valid as Hemigrammus orthus Durbin 1909 -- (Lima & Oyakawa in Reis et al. 2003:133 [ref. 27061], Bertaco & Carvalho 2005:147 [ref. 28675], Zarske et al. 2006:30 [ref. 28749], Carvalho et al. 2010:253 [ref. 30862], Taphorn et al. 2022:15 [ref. 41297]). Current status: Valid as Hemigrammus orthus Durbin 1909. Acestrorhamphidae: Pristellinae. Distribution: South America: Essequibo River (Guyana); lower Tapajós River (Brazil). Habitat: freshwater.