THE RULES OF NOMENCLATURE 361 



(a) given the same name to different genera, or to different 

 species of the same genus, either through a mistake in 

 identification or in ignorance that the name was already 

 in use ; (b) given different names to the same genus or 

 species ; (c) divided up an existing genus into several 

 genera, or (d) united distinct genera into one. 



The most general rule in all nomenclature is the law of 

 priority, according to which, other things being equal, 

 the earliest name given to any genus or species must 

 stand : all later names are synonyms, and as such are 

 rejected. To this rule there are certain necessary quali- 

 fications : 



1. The name must have been published i.e., printed 

 and circulated so as to be accessible to the public, and it 

 must have been accompanied by either a description 

 (diagnosis) or a figure (or both) which would make it 

 possible to identify the species to which the name was 

 applied. In the case of a new genus, a diagnosis is not 

 absolutely necessary, if the type-species is given. 



2. It must have been applied in accordance with the 

 Linnaean system. This rules out all names published 

 prior to the year 1758 (date of the tenth edition of the 

 Systema Nature of Linnaeus) even if they are binominal 

 in form ; for in pre-Linnaean names that form is accidental, 

 the earlier method having been to give a generic name 

 followed by what was really not a trivial name but a 

 description or diagnosis (though occasionally a single 

 adjective sufficed). 



3. That the same name has not already been applied 

 if generic, to some other genus ; if trivial, to some other 

 species of the same genus. In case of such previous 

 application the name (in its new application) is a homonym. 

 Thus the name Avalonia was given by Walcott in 1889 to 

 a genus of trilobites ; the same name was applied by 

 Seeley in 1898 to a reptile. Hence Avalonia Seeley, 1898, 



