Article 42. The genus group
The genus group, which is next below the family group and next above the species group in the hierarchy of classification, encompasses all nominal taxa at the ranks of genus and subgenus (see also Articles 10.3 and 10.4).
42.2. Provisions applicable to all genus-group nominal taxa and their names
Genus-group nominal taxa and their names are subject to the same provisions whatever their rank, except when these apply explicitly at one rank alone.
42.2.1. The names established expressly for certain assemblages of taxonomic convenience known as "collective groups" and names for trace fossils (ichnotaxa) established at the genus-group level are to be treated as genus-group names in the meaning of the Code [Art. 10.3], unless there is a statement to the contrary in a particular Article (as in Articles 13.3.2, 13.3.3, 23.7, 42.3.1, 66, 67.14); each takes its original author and date.
Examples. (a) Of a collective group name: Agamofilaria Stiles, 1907 (Nematoda). (b) Of names proposed for trace fossils: Helicolithus Azpeitia Moros, 1933 and Stelloglyphus Vyalov, 1964.
42.3. Application of genus-group names
The application of each genus-group name is determined by reference to the type species [Arts. 61, 66 to 70] of the nominal taxon that it denotes.
42.3.1. Collective groups have no type species (see also Articles 13.3.2 and 67.14).
42.3.2. Nominal taxa of the genus group established before 1931 (in the case of ichnotaxa, before 2000 [Art. 13.3.3]) may have had no type species fixed; in such cases Article 69 applies.
42.4. Formation and treatment of genus-group names
A genus-group name is to be formed and treated in accordance with Articles 10.3, 10.4 and 11.8, and the relevant provisions of Articles 25 to 33.