The International Code of Nomenclature of Prokaryotes provides rules that govern the way names are to be selected based on priority of valid publication when two or more alternatives (synonyms) are available. However, these rules are not always followed. In the case of the name CaryophanaceaePeshkoff 1939 (Approved Lists 1980), when its nomenclatural type CaryophanonPeshkoff 1939 (Approved Lists 1980) is placed in the same taxon as PlanococcusMigula 1894 (Approved Lists 1980), the nomenclatural type of PlanococcaceaeKrasil'nikov 1949 (Approved Lists 1980), then the two are considered to be heterotypic synonyms and the name which has priority is CaryophanaceaePeshkoff 1939 (Approved Lists 1980). Similarly in the case of the name CaryophanalesPeshkoff 1939 (Approved Lists 1980) when its nomenclatural type CaryophanonPeshkoff 1939 (Approved Lists 1980) is placed in the same taxon as Bacillus Cohn 1872 (Approved Lists 1980), the nomenclatural type of BacillalesPrévot 1953 (Approved Lists 1980), then the two are considered to be heterotypic synonyms and the name which has priority is CaryophanalesPeshkoff 1939 (Approved Lists 1980) While the rules of the International Code of Nomenclature of Prokaryotes are unambiguous in determining the correct names despite the fact that the names CaryophanaceaePeshkoff 1939 (Approved Lists 1980) and CaryophanalesPeshkoff 1939 (Approved Lists 1980) are rarely used.