Diagnosis: Distinguished from its congeners by the following unique characters: an unusual electric organ (EO) morphology in which the posterior EO margin ends abruptly and is replaced by rigid and transparent non-electrogenic tissue in the posterior, approximate one-half of the caudal appendage; very visible hemal spines in the posterior half of the caudal appendage; presence of 5 (vs. 6 or 7) pairs of pleural ribs; oral teeth conical, with diameter at base more than at midlength (vs. villiform, about as wide at base as at midlength in all congeners; cleithral posterior process broad (vs. narrow in all congeners). Also, it differs from its congeners, except with R. stewarti, in possessing non-ossified gill rakers, and except R. electrogrammus and R. caviceps, in possessing a distinct "black cap" (dense region of dark chromatophores in the parietal region) (Ref. 55969).