Article 68. Type species fixed in the original publication
If one (or more) species qualifies for fixation as the type species in more than one of the ways provided for in Articles 68.2-68.5, the valid fixation is that determined by reference to the following order of precedence: firstly, original designation [Art. 68.2], then monotypy [Art. 68.3], then absolute tautonymy [Art. 68.4], and lastly Linnaean tautonymy [Art. 68.5].
Recommendation 68A. Citation of type fixation. If a species is qualified for fixation as the type species in more than one of the ways provided for in this Article, only the valid fixation need be cited.
If one nominal species is explicitly designated [Art. 67.5] as the type species when a nominal genus-group taxon is established, that nominal species is the type species (type by original designation) unless the provisions of Article 70.3 apply.
68.2.1. The expressions "gen. n., sp. n.", "new genus and species", or an equivalent, applied before 1931 to only one of two or more new nominal species originally included in a new nominal genus or subgenus, are deemed to be an original designation if no other type species was explicitly designated.
68.2.2. If, when a nominal genus-group taxon is established without explicit designation of a type species, one originally included new nominal species [Art. 67.2] is given the species-group name typicus, -a, -um or typus, that nominal species is deemed to be the type species by original designation.
When an author establishes a new nominal genus-group taxon for a single taxonomic species and denotes that species by an available name, the nominal species so named is the type species. Fixation by this means is deemed to be fixation by monotypy, regardless of any cited synonyms, subspecies, or unavailable names, and regardless of whether the author considered the nominal genus-group taxon to contain other species which he or she did not cite by name, and regardless of nominal species-group taxa doubtfully included or identified.
68.3.1. If a new genus is divided into subgenera at the time its name is established, and if the nominotypical subgenus contains only a single species, that nominal species is deemed to be the type by monotypy of the new nominal genus.
If a valid species-group name, or its cited synonym, originally included [Art. 67.2] in a nominal genus-group taxon is identical with the name of that taxon, the nominal species denoted by that specific name (if available) is the type species (type species by absolute tautonymy).
Example. The new nominal genus Aus Smith contains among its nominal species Aus xus (Brown); among the cited synonyms of the latter is the available name Bus xus aus Robinson. The type species of Aus is Bus aus Robinson, not Bus xus Brown.
If, in the synonymy of only one of the originally included nominal species [Art. 67.2] in a nominal genus-group taxon established before 1931, there is cited a pre-1758 name of one word identical with the new genus-group name, that nominal species is the type species (type species by "Linnaean tautonymy").
Example. The genus Castor Linnaeus, 1758 (the beaver) was established with two included species. In the synonymy of one of these species (Castor fiber) is cited the one-word name "Castor Gesner pisc. 185." Castor fiber Linnaeus, 1758 is therefore the type species of Castor by Linnaean tautonymy.