Article 59. Validity of secondary homonyms.
59.1. Taxa considered congeneric. A species-group name while a junior secondary homonym must be treated as invalid by anyone who considers that the two species-group taxa in question are congeneric.
59.2. Secondary homonyms not replaced when no longer considered congeneric. If in a case of secondary homonymy the junior species-group name has not been replaced [Art. 60], and the relevant taxa are no longer considered congeneric, the junior name is not to be rejected, even if one species-group name was originally proposed in the current genus of the other.
Example. Zetterstedt (1855) established the new species Platyura nigriventris, which is now placed in the genus Orfelia. In 1910 Johannsen established the new species Apemon nigriventris, which was later referred to Platyura, its present position. The two species are not now treated as congeneric, and inasmuch as nigriventris (Johannsen) was never renamed in Platyura, a substitute name is not necessary.
59.3. Secondary homonyms replaced before 1961 but no longer considered congeneric. A junior secondary homonym replaced before 1961 is permanently invalid unless the substitute name is not in use and the relevant taxa are no longer considered congeneric, in which case the junior homonym is not to be rejected on grounds of that replacement.
Example. Deignan (1947) on taxonomic grounds merged the avian genera Muscicapa Brisson, 1760, Ficedula Brisson, 1760 and Niltava Hodgson, 1837 and took the first name as valid. He replaced seven resulting junior secondary homonyms, but because his classification and substitute names are not in use the species-group names that were replaced are not to be rejected under this Article.
59.3.1. If the use of a substitute name for a junior secondary homonym is a cause of confusion, the case is to be referred to the Commission for a ruling (under the plenary power if necessary, see Article 81) as to which name will, in its judgment, best serve stability and universality, and that name is then the valid name.
59.4. Reinstatement of junior secondary homonyms rejected after 1960. A species-group name rejected after 1960 on grounds of secondary homonymy is to be reinstated as valid by an author who considers that the two species-group taxa in question are not congeneric, unless it is invalid for some other reason.
Example. Aus niger Smith, 1950, if transferred after 1960 to Bus, becomes a junior secondary homonym of Bus niger Dupont, 1940, and is renamed Bus ater Jones, 1970. However, an author who does not consider that the two species are congeneric is to reinstate niger Smith as the valid specific name for the species concerned, with ater Jones as a junior synonym.