A review of the Malagasy Pachypanchax (Teleostei: Cyprinodontiformes, Aplocheilidae), with descriptions of four new species. Paul V. Loiselle Zootaxa 2006 1366 1 44 6BX9 52662 urn:lsid:zoobank.org:act:F37E2B4C-B726-4D09-B675-CB3E4082BD81 Aplocheilidae Pachypanchax CoL Animalia Pachypanchax Myers 1933:1 Cyprinodontiformes 2 Chordata genus  Introduction Myers (1933) established the genus Pachypanchaxfor Haplochilus playfairii Guenther, 1866, a robust killifish endemic to the granitic Seychelles (Playfair and Guenther, 1866). He included two Malagasy species, Poecilia omalonota Dumeril, 1861and Panchax sakaramyi Holly, 1928in his new genus. This attribution appears to have been made on biogeographic grounds, as Myers clearly indicated that he had not examined specimens of either Malagasy species. Scheel (1968) refined Myer’s definition of the genus with the addition of two additional diagnostic characters. However, the material of P. omalonotaavailable to Scheel consisted of aquarium-reared specimens descended from fish collected from the lower reaches of the westward-flowing Betsiboka River, on the mainland of Madagascar (Arnoult, 1955), whereas the type material of P. omalonotusactually came from the island of Nosy Be, off northwestern Madagascar. Subsequent collecting has demonstrated these two taxa differ sufficiently in coloration and morphology to warrant recognition as separate species. Parenti (1981) subsequently redefined the genus, placing particular emphasis upon several skeletal apomorphies. However, Parenti neither examined topotypical material of P. omalonotusnor specimens of the other two nominal Malagasy species, P. sakaramyiand P. nuchimaculatus (Guichenot, 1866). Her inclusion of the Malagasy species within the genus was thus tentative. Fieldwork in Madagascar undertaken since 1993 has resulted in the collection of larger series of both P. omalonotusand P. sakaramyi, and in the discovery of additional aplocheilid taxa that cannot be referred to previously published nomina. In light of these discoveries, it is appropriate to reexamine Parenti’s definition of the genus Pachypanchax, redescribe P. omalonotusand P. sakaramyi, and describe four of these new taxa. Three more recently discovered Malagasy species remain to be described.