Article 64. Choice of type genus. An author who wishes to establish a new nominal family-group taxon may choose as type genus any included nominal genus the name of which he or she regards as valid [Art. 11.7.1], not necessarily that having the oldest name. The choice of type genus determines the stem of the name of the nominal family-group taxon [Art. 29.1].
Recommendation 64A. Type genus should be well known. So far as possible, an author who wishes to establish a nominal family-group taxon should choose as its type genus a genus that is both well known and representative of the family-group taxon.