Three genera are recognized in the family Potamotrygonidae of neotropical freshwater stingrays: Potamotrygon, Paratrygon, and Plesiotrygon, the latter being described as a new genus. Potamotrygon is polytypic, and both Paratrygon and Plesiotrygon are monotypic, as far as known. The family name Potamotrygonidae has priority over Paratrygonidae Gill. Nineteen previously described species of Potamotrygonidae are recognized: Paratrygon aiereba, Potamotrygon brachyura, P. castexi, P. constellata, P. dumerilii, P. falkneri, P. henlei, P. histrix, P. humerosa, P. leopoldi, P. magdalenae, P. motoro, P. ocellata, P. orbignyi, P. schroederi, P. schuemacheri, P. scobina, P. signata, and P. yepezi. One additional specific name is established as new (Plesiotrygon iwamae). Three of the eighteen recognized species of Potamotrygon are resurrected from synonymy (P. dumerilii, P. henlei, and P. orbignyi), one previously overlooked subspecific name (Trygon histrix ocellata) is erected to specific rank, and one previously overlooked specific name (Taeniura constellata) is placed in the genus Potamotrygon, and treated as a senior synonym of P. circularis. The remaining names previously assigned to the Potamotrygonidae include: eight junior synonyms (Disceus thayeri, Potamotrygon brumi, P. circularis, P. laticeps, P. menchacai, Trygon mulleri, T. reticulatus, and T. strogylopterus), five doubtful names (Elipesurus spinicauda, Potamotrygon africana, P. alba, P. humboldtii, and Trygon garrapa), two invalid names (Potamotrygon labratoris and P. pauckei), two doubtful names corresponding to one unidentified marine species of the family Dasyatididae (Raja ajereba and R. orbicularis), and one freshwater species of Dasyatis (D. garouaensis) originally described in the genus Potamotrygon. Potamotrygon and Paratrygon are regarded as sister groups, and Plesiotrygon as the primitive potamotrygonid genus, based on a cladistic analysis of stingray characters. Plesiotrygon is restricted to the upper Amazon drainage, and Paratrygon is known from most of the Amazon drainage, occurring also in Rio Orinoco. Eleven species of Potamotrygon have Amazonian distribution (including Rio Tocantins), four of which occur also in other drainages. Four species of Potamotrygon are apparently endemic to Rio Paraguay and lower Rio Parana drainages (P. brachyura, P. falkneri, P. histrix, and P. schuemacheri); P. yepezi is endemic to the Maracaibo basin in Venezuela; P. magdalenae is endemic to Rio Magdalena and Rio Atrato drainages in Colombia, and P. signata is apparently endemic to Rio Parna(')iba drainage in Brazil.

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