The recent examination of the holotypes of Callichthys thoracatus and Callichthys longifilis led to important modifications in the nomenclature of the two species of Megalechis. Inspection of these holotypes demonstrated that they represent the species that has commonly been referred to in current literature as Megalechis personata. Because C. thoracatus is an older name than C. personatus, it has priority and is considered as the senior synonym. Callichthys pictus is the oldest name applicable to the species commonly referred to in current literature as Megalechis thoracata, and is thus the valid name. Rearranged synonymies, updated diagnoses, and illustrations are provided for both species of Megalechis.