A revision of the South American killifish genus Simpsonichthys published in a recent issue of the journal Zootaxa recognizes 50 species.
The study by Wilson Costa describes the 50 valid species in five subgenera.
Xenurolebias, from the coastal plains of eastern Brazil, includes only S. myersi.
Ophthalmolebias, from the coastal river basins of eastern and southeastern Brazil, comprises S. constanciae, S. suzarti, S. bokermanni, S. perpendicularis, and S. rosaceus.
Simpsonichthys, from the central Brazilian plateau, in the upper Paran, upper Araguaia and upper So Francisco river basins, comprises S. cholopteryx, S. parallelus, S. nigromaculatus, S. punctulatus, S. boitonei, S. santanae, and S. zonatus.
Spectrolebias, from the Middle Tocantins, middle Araguaia, Xingu, Mamor, and Paraguay river basins, in Brazil, Bolivia and Paraguay, includes S. reticulatus, S. costai, S. chacoensis, S. filamentosus, and S. semiocellatus.
Hypsolebias, from the So Francisco, Tocantins, Middle Jequitinhonha and lower Jaguaribe river basins and isolated coastal basins of northeastern Brazil, comprising S. ocellatus, S. rufus, S. stellatus, S. nielseni, S. notatus, S. radiosus, S. similis, S. gibberatus, S. virgulatus, S. trilineatus, S. auratus, S. hellneri, S. adornatus, S. fulminantis, S. carlettoi, S. magnificus, S. picturatus, S. antenori, S. macaubensis, S. mediopapillatus, S. ghisolfii, S. igneus, S. flavicaudatus, S. flagellatus, S. janaubensis, S. marginatus, S. delucai, S. alternatus, S. fasciatus, S. multiradiatus, S. flammeus, and S. brunoi.
The study redescribes all 50 species in detail, and provides identification keys.
For more information, see the paper: Costa, WJEM (2007) Taxonomic revision of the seasonal South American killifish genus Simpsonichthys (Teleostei: Cyprinodontiformes: Aplocheiloidei: Rivulidae). Zootaxa 1669, pp. 1"134.