Article 74. Name-bearing types fixed subsequently from the type series (lectotypes from syntypes)
A lectotype may be designated from syntypes to become the unique bearer of the name of a nominal species-group taxon and the standard for its application (except in the case of hapantotypes [Art. 73.3]).
74.1.1. The valid designation of a lectotype fixes the status of the specimen as the sole name-bearing type of that nominal taxon; no later designation of a lectotype has any validity.
74.1.2. The valid designation of a lectotype supersedes any previous restriction of the application of the name of the taxon.
74.1.3. The valid designation of a lectotype permanently deprives all other specimens that were formerly syntypes of that nominal taxon of the status of syntype [Art. 73.2.2]; those specimens then become paralectotypes.
If it is demonstrated that a specimen designated as a lectotype was not a syntype, it loses its status of lectotype.
Lectotypes must not be designated collectively by a general statement; each designation must be made specifically for one nominal taxon and must have as its object the definition of that taxon.
Example. Smith, revising collections described in publications by Dupont, made the statement that in the case of each new species described by Dupont "the specimen bearing the author's determination label is the type" or "the specimen listed first in the publication is designated as the lectotype". Such an act by Smith does not constitute valid lectotype designation.
Designation of an illustration or description of a syntype as a lectotype is to be treated as designation of the specimen illustrated or described; the fact that the specimen no longer exists or cannot be traced does not of itself invalidate the designation.
In a lectotype designation made before 2000, either the term "lectotype", or an exact translation or equivalent expression (e.g. "the type"), must have been used or the author must have unambiguously selected a particular syntype to act as the unique name-bearing type of the taxon. When the original work reveals that the taxon had been based on more than one specimen, a subsequent use of the term "holotype" does not constitute a valid lectotype designation unless the author, when wrongly using that term, explicitly indicated that he or she was selecting from the type series that particular specimen to serve as the name-bearing type.
When it has been accepted that a nominal species-group taxon was based on a single specimen and the original description neither implies nor requires that there were syntypes, and if it is considered subsequently that the original description was based on more than one specimen, the first author to have published before 2000 the assumption that the species-group taxon was based upon a single type specimen is deemed to have designated that specimen as the lectotype.
74.6.1. The inference that the specimen is a "holotype" or "the type"
126.96.36.199. may be by reference to an illustration or description of a specimen [Art. 74.4];
188.8.131.52. must be individual in accordance with Article 74.3.
Example. The fossil marsupial "lion" Thylacoleo carnifex Owen, 1858 was described briefly in the Encyclopaedia Britannica. The description included a figure of a cranium. Although the lower dentition was mentioned, there was no information that it did not form part of the same specimen. McCoy (1876) described a new nominal species Thylacoleo oweni, stating at the same time that the cranium described by Owen was "the first described type of the species" T. carnifex. The cranium has been accepted universally as the holotype. It is now known that the original description contained information partly based upon a portion of a mandible from a different locality. McCoy's (1876) inference that the cranium is "the type" is deemed to constitute lectotype fixation.
To be valid, a lectotype designation made after 1999 must
74.7.1. employ the term "lectotype" or an exact translation (e.g. "lectotypus", but not "the type"),
74.7.2. contain information sufficient to ensure recognition of the specimen designated, and
74.7.3. contain an express statement of the taxonomic purpose of the designation.
74.7.3. contain an express statement of deliberate designation (merely citing a specimen as "lectotype" is insufficient).
Example. A statement such as "lectotype hereby designated", "lectotype by present designation", "I choose specimen X as lectotype" would fulfil this requirement, but "lectotype: specimen X" would not.
Recommendation 74A. Agreement with previous restriction. In designating a lectotype, in order to preserve stability of nomenclature an author should act consistently with, and in any event should give great weight to, previously accepted taxonomic restrictions of the application of the name.
Recommendation 74B. Preference for illustrated specimen. Other things being equal, an author who designates a lectotype should give preference to a syntype of which an illustration has been published.
Recommendation 74C. Data on the lectotype. An author who designates a lectotype should publish for it the data listed in Recommendation 73C, besides describing any individual characteristics by which it can be recognized.
Recommendation 74D. Choice between syntypes in several collections. When possible, a lectotype should be chosen from syntypes in the collection of a public institution, preferably of the institution containing the largest number of syntypes of the nominal species-group taxon, or containing the collection upon which the author of the nominal species-group taxon worked, or containing the majority of that author's types.
Recommendation 74E. Verification of locality. When selecting a lectotype, the author should, if possible, verify the accuracy of the locality ascribed to it. A syntype of known locality should be preferred to one of unknown origin.
Recommendation 74F. Paralectotypes. An author who designates a lectotype should clearly label other former syntypes as "paralectotypes". Like paratypes, paralectotypes have no name-bearing status, but they are eligible for designation of neotypes.
Recommendation 74G. Not merely for curatorial purposes. The designation of lectotypes should be done as part of a revisionary or other taxonomic work to enhance the stability of nomenclature, and not for mere curatorial convenience.