Bacteria and Viruses 83 



Rules 18a, 18b. Sect. 5. Changes in Names of Taxa 



RULE 18a. When a species is divided into two or more species, the specific 

 epithet must be retained for one of them, or (if it has not been retained) 

 must be reinstated. When a type has been designated for the species, the 

 specific epithet must be retained for the species including that type. When 

 no type was designated, one must be chosen. 



The same rule applies to subspecies (varieties); for example, to a sub- 

 species (variety) divided into two or more subspecies (varieties). 

 RULE 18b. When a species is transferred to another genus (or placed under 

 another generic name for the same genus), without change of rank, the 

 specific epithet must be retained or (if it has not been retained) must be re- 

 established unless one of the following obstacles exists: (1) the resulting 

 binary name is a later homonym or tautonym or (2) there is available an 

 earlier validly published specific epithet. 



When the specific epithet, on transference to another generic name, has 

 been applied erroneously in its new position to a difFerent species, the new 

 combination must be retained for the organism on which the epithet was 

 originally based. 



ANNOTATIONS 



Rule 18a. Example: Frank (1890) named Rhizobhim leguminosarum 

 as the single species of the genus to include the bacteria responsible 

 for nodulation of the roots of leguminous plants. Baldwin and Fred 

 (1929) recognized several species described from the roots of different 

 legumes. They rightly retained the name Rhizohium leguminosarum 

 Frank as the type species to include the bacteria from species of 

 Lathyrus and related genera. 



The rule in botany is essentially the same. 



The corresponding Article in the Zoological Rules states that 

 when a nominal species (or a subspecies) is divided into two or more 

 restricted species (or subspecies) the division is governed by the 

 same Rules as in the division of a genus. 



