Article 69. Type species not fixed in the original publication
If a nominal genus-group taxon was established before 1931 (in the case of an ichnotaxon, before 2000) and no type species was fixed in the original publication [Art. 68], the provisions of this Article apply subject, when appropriate, to the provisions of Article 70.2 and 70.3.
If an author established a nominal genus or subgenus but did not fix its type species, the first author who subsequently designates one of the originally included nominal species [Art. 67.2] validly designates the type species of that nominal genus or subgenus (type by subsequent designation), and no later designation is valid.
69.1.1. In the absence of a prior type fixation for a nominal genus or subgenus, an author is deemed to have designated one of the originally included nominal species as type species, if he or she states (for whatever reason, right or wrong) that it is the type or type species, or uses an equivalent term, and if it is clear that that author accepts it as the type species.
69.1.2. A subsequent designation first made in a literature-recording publication is to be accepted, if valid in all other respects.
An originally included nominal species is eligible for subsequent fixation as type species even if it is the type species of another genus-group taxon [Art. 67.11] or had been included in another such taxon.
69.2.1. If an author subsequently designates a type species by using an unjustified emendation or an incorrect spelling of the name of one of the originally included nominal species, he or she is deemed to have designated the type species under its correctly spelled name [Art. 67.6].
69.2.2. If an author designates as type species a nominal species that was not originally included (or accepts another's such designation) and if, but only if, at the same time he or she places that nominal species in synonymy with one and only one of the originally included species (as defined in Article 67.2), that act constitutes fixation of the latter species as type species of the nominal genus or subgenus.
69.2.3. If an author designates a type species denoted by a new replacement name (nomen novum) for the name of an originally included species, that act constitutes fixation of that originally included nominal species as the type species of the nominal genus or subgenus.
69.2.4. If an author subsequently designates as type species a species originally included [Art. 67.2.1] as an expressly stated misidentification or misapplication of a previously established nominal species, the species so designated is the nominal species denoted by the name of the taxonomic species actually involved (and not the nominal species cited).
If only one nominal species was first subsequently included in a nominal genus or subgenus established without included species, that nominal species is automatically fixed as the type species, by subsequent monotypy.
Elimination of all but one of the originally included nominal species from a nominal genus or subgenus does not in itself constitute type fixation.
Recommendation 69A. Criteria of preference. In designating a type species for a nominal genus or subgenus, an author should give preference to a species that is adequately described or illustrated, or of which type material still exists, or of which material is easily obtained. When these properties are shared by more than one species, an author should be guided by the following criteria, in order of preference:
69A.1. The most common species, or one of medical or economic importance, or one with the specific name communis, vulgaris, medicinalis, or officinalis, should be designated.
69A.2. If the valid name or a synonym of one of the originally included nominal species includes a species-group name virtually the same as the name of the genus-group taxon, or that is of the same derivation or meaning, that species should be designated as the type species (choice resulting from "virtual tautonymy"), unless such designation is strongly contra-indicated by other factors.
Examples. Bos taurus, Equus caballus, Ovis aries, Scomber scombrus, Sphaerostoma globiporum, Spinicapitichthys spiniceps.
69A.3. If some of the originally included nominal species have been removed to other nominal genus-group taxa, preference should be given to a remaining species, if any such is suitable ("choice following elimination").
69A.4. A nominal species having a sexually mature specimen as its type is generally preferable to one based on a larval or otherwise immature specimen.
69A.5. If more than one group of species is recognized in a nominal genus-group taxon, preference should be given to a nominal species that belongs to as large a group as possible.
69A.6. In genus-group taxa of parasites, preference should be given to a nominal species that parasitizes humans or an animal of economic importance or a common and widespread host species.
69A.7. All other things being equal, preference should be given to a nominal species well known to the author of the nominal genus-group taxon at the time he or she established it.
69A.8. If an author is known to have habitually placed a "typical" (i.e. representative) species first and described others by comparison with it, that fact should be considered in the designation of a type species.
69A.9. If an author is known to have denoted type species by their position ("first species rule"), the first nominal species cited by him or her should be designated as the type species.
69A.10. All other things being equal, preference should be given to the nominal species cited first in the work, page or line ("position precedence").