Article 55. Family-group names.

55.1. Application of the Principle of Homonymy. The Principle of Homonymy applies to all family-group names, including names of ichnotaxa at the family-group level.

55.2. Homonymy from identical generic names. See Article 39.

55.3. Homonymy from similar generic names. Homonymy between family-group names may result from similarity but not identity of the names of their type genera.

55.3.1. Such a case involving family-group names must be referred to the Commission for a ruling to remove homonymy unless the senior homonym is a nomen oblitum.

55.3.1.1. When the senior homonym is determined to be a nomen oblitum under the conditions of Article 23.9.2, a new family-group name (a nomen novum) based on the same type genus may be proposed, but choosing a new stem from the name of the type genus which avoids the homonymy [Arts. 29.1, 29.4 and 29.6].

55.4. One-letter difference. Even if the difference between two family-group names is only one letter, they are not homonyms.

Example. The family names LARIDAE (Aves), based on Larus Linnaeus, 1758, and LARRIDAE (Hymenoptera), based on Larra Fabricius, 1793, differ by one letter and are not homonyms.

55.5. Precedence of names at higher rank. Of two homonymous family-group names of identical date but established at different ranks, the one established at the higher rank is deemed to be the senior homonym [Art. 24.1].