RULES OF XOMEXCLATURE 61 



concept as a means of defining bacterial genera, the reader is referred to the 

 A\Titings of Hitchcock (Amer. Jour. Bot., 8, 1921, 251; Descriptive Sys- 

 tematic Botany, New York, 1925) for an excellent exposition of the value of 

 this idea to systematists. 



Hitchcock (1921, p. 252) explains this concept briefly as follows: "The 

 old concept was that a genus was a group of species having a given com- 

 bination of characters ; a species, similarly, a group of specimens. The new 

 type concept is that, from the nomenclatural standpoint, a genus is a group 

 of species allied to the type species; a species, a group of individuals similar 

 to the type specimen." 



Rules for determining types taken from the Type Basis Code of Nomen- 

 clature (Science, 45, 1919, 333; -53, 1921, 312) drawn up by a Committee of 

 which Hitchcock was Chairman are quoted as these are the most authori- 

 tative rules thus far available. 



Type Basis Code of Nomenclatvre {Hitchcock el al.) 



Article 4. The nomenclatural type species of a genus is the species or one of the 

 species included when the genus was originally published. 



If a genus included but one species when originally published, this species is the 

 type. 



When more than one species is included in the original publication of the genus, the 

 type is determined by the following rules: 



(a) When, in the original publication of a genus, one of the species is definitely 

 designated as type, this species shall be accepted as the type regardless of other con- 

 siderations. 



If typicus or typus is used as a new specific name for one of the species, this species 

 shall be accepted as the type as if it were definitely' designated. 



(b) The publication of a new generic name as an avowed substitute for an earlier 

 one does not change the type of the genus. 



(c) If a genus, without an originally designated type, contains among its original 

 species one with the generic name used as a specific name, either as a valid name or 

 synonym, that species is to be accepted as the type. 



(d) If a genus, when originally published, includes more than one species, and no 

 species is definitely designated as type, nor indicated according to (c), the choice of 

 the type should accord with the following principles: 



1. Species inquirendae or species doubtfully referred to the genus, or mentioned 



as in any way e.xceptional are to be excluded from consideration in selecting 

 the type. 



2. Genera of the first edition of Linnaeus's "Species Plantarum" (1753) 



are usually typified through the citations given in the fifth edition of his 

 "Genera Plantarum" (1754) except when inconsistent with the preceding 

 articles. 



3. Species which definitely disagree with the generic description (provided others 



agree), or which possess characters stated in the generic description as rare 

 or unusual, are to be excluded from consideration in selecting the type. 



