On the priority between Yokenella regensburgei Kosako et al. 1985 and Koserella trabulsii Hickman-Brenner et al. 1985 and on the priority between Providencia alcalifaciens (de Salles Gomes 1944) Ewing 1962 (Approved Lists 1980) and Proteus inconstans

In this paper, I include two Requests for an Opinion regarding ambiguous priority of pairs of names considered synonyms. First, I present a case of unknown priority between heterotypic synonyms <i>Yokenella regensburgei</i> Kosako <i>et al</i>. 1985 and <i>Koserella trabulsii</i> Hickman-Brenner <i>et al</i>. 1985. These two names appeared on the same Validation List but without any sequence number given. According to Rule 24b(4) of the 2022 Revision of the International Code of Nomenclature of Prokaryotes (ICNP), in the case of no sequence numbers given, it is up to those who first propose union of the taxa to determine the priority. However, no choice was made by those who synonymized these two names, and therefore, it is impossible to choose the correct name. To resolve this extremely rare, awkward situation, I argue that the Judicial Commission should conserve the genus name and epithet of the well-known name <i>Y. regensburgei</i> over those of the less-known <i>K. trabulsii</i> according to Rule 56b of the ICNP. And by doing this, <i>Y. regensburgei</i> will become the correct name for the united taxon with this particular circumscription. Secondly, I discussed the case in which <i>Providencia alcalifaciens</i> (de Salles Gomes 1944) Ewing 1962 (Approved Lists 1980) and <i>Proteus inconstans</i> (Ornstein 1920) Shaw and Clarke 1955 (Approved Lists 1980) are found to be homotypic synonyms both included in the Approved Lists. Based on the priority, <i>inconstans</i> in <i>P. inconstans</i> is the earliest epithet to be adopted in the correct name, which means that <i>alcalifaciens</i> in <i>P. alcalifaciens</i> should be treated as an illegitimate epithet. Since <i>P. alcalifaciens</i> was proposed as the type species of the genus <i>Providencia</i>, the generic name and any of its combinations are illegitimate as well according to Rules 20a and 51b(2) of the ICNP. Literature search showed that the name <i>Proteus inconstans</i> has become obsolete and <i>Providencia alcalifaciens</i> is in prevailing usage. Moreover, 16 validly published names, including synonyms, have been proposed to date under the genus <i>Providencia</i>. Accordingly, I argue that the necessary conservation of the epithet <i>inconstans</i> in <i>P. inconstans</i> over <i>alcalifaciens</i> in <i>P. alcalifaciens</i> should be made by the Judicial Commission according to Rule 56b for the sake of nomenclatural stability.