Culex chrysothorax (Newstead Thomas, 1910) (Diptera: Culicidae) is recognized as the junior secondary homonym of Culex chrysothorax (Peryass, 1908). Both nominal species are currently regarded as nomina dubia (Pecor et al. 1991; Harbach 2018; Wilkerson et al. 2021). Based on critical examination of the lectotype female, the former nominal species, which was treated as species inquirenda by Forattini Sallum (1989), is no longer regarded as a doubtful species, and is found to be conspecific with Cx. trigeminatus Clastrier, 1970. Because it is preoccupied by Cx. chrysothorax (Peryass, 1908), it is placed in synonymy with Cx. trigeminatus, which is transferred from the Educator to the Atratus Group of the subgenus Melanoconion based on morphological features of the female. Culex chrysothorax (Peryass, 1908) is retained in the Educator Group as a nomen dubium. Because the original description of Cx. chrysothorax (Newstead Thomas) likely included misidentified specimens of Cx. theobaldi (Lutz, 1904), a more precise description of the lectotype female is provided.