The electric fish genus Platyurosternarchus, family Apteronotidae, is reviewed based on both external morphology and osteology. Synapomorphies for Platyurosternarchus are identified, the genus is diagnosed, and a key to the species is provided. Platyurosternarchus crypticus, a new species, is described from the upper reaches of the Rio Branco in the northern portions of the Amazon basin. Platyurosternarchus macrostoma from the Amazonas, Orinoco, and Essequibo River basins is redescribed. The species differ in the form of the laterosensory canal segment in the soft tissues of the ventral portion of the head and within the preopercle, the posterior extent of the mid-dorsal electroreceptive filament, and the morphology of the first and fourth branchiostegal rays.