The purpose of this application, under Article 23.9.5 of the ICZN Code, is to conserve the specific name Gyrinus (Enhydrus) australis Brullé, 1835 (currently Macrogyrus (Macrogyrus) australis), which is threatened by Gyrinus australis Fabricius, 1775 (currently Dineutus (Cyclous) australis) (both in Gyrinidae, Gyrininae, Dineutini). Although the names were transferred out of the genus Gyrinus Geoffroy, 1762 and have never been treated as congeneric, they are nevertheless primary homonyms. The Fabrician name has been treated as valid since it was proposed, was combined with the generic name Cyclous by Dejean, and has always been placed in Dineutus since its transfer to this genus by Aubé in 1838—with the exception of a single work of Motschulsky, where it was given again in Cyclous. After its publication, Brullé's name was never again given in combination with the generic name Gyrinus and was not accepted as a valid name during a period of almost 60 years. Only Régimbart treated the name as valid in 1892, and it has since always been placed in the genus Macrogyrus Régimbart, 1892. It is proposed that Gyrinus australis Brullé, 1835 be conserved by ruling that it is not invalid by reason of being a junior homonym of Gyrinus australis Fabricius, 1775.