Schizodon scotorhabdotus is described from the Río Orinoco system of Venezuela and Colombia. Its most similar congener, S. isognathus, is redescribed from the Río Paraguay system of Brazil, Bolivia, and Paraguay, and a lectotype is designated for the species. Schizodon scotorhabdotus and S. isognathus can be distinguished from each other and from the most similar congener, S. knerii, by circumpeduncular and transverse scale counts, jaw orientation and osteology, and details of coloration. A principal components-based comparison of S. isognathus, S. knerii, and S. scotorhabdotus revealed that the three cited species also differ in mean body shape, particularly in body width. Comments are included on geographic distribution, life coloration, diet, and ontogenetic variation, including notable shifts in mouth position and caudal-fin morphology of these species.