Contributions to the taxonomy of the genera Pachysternum and Cyrtonion (Coleoptera, Hydrophilidae, Sphaeridiinae)

Pachysternum loxodonta sp. n. from the Republic of the Congo and Pachysternum sulawesicum sp.n. from Sulawesi Island, Indonesia are described. The generic status of Pachysternum sculpticolle (Régimbart, 1907) is revised, the species is transferred to the genus Cyrtonion and its differences from C. ghanense Hansen, 1989 are discussed. Taxonomy of Pachysternum is discussed, dividing the genus prelusively into three species groups, one comprising all known Oriental and Eastern Palearctic species, and two comprising the Afrotropical species. Species with unclear positions within the genus Pachysternum or with questionable generic status are left as “Species incertae sedis”.