THE RULES OF NOMENCLATURE 369 



Phacops, and Ptevygometopus. It will be noted that the 

 genus Phacops is typical both of the whole family and of 

 one of the sub-families. 



As there have been many cases where opinions have 

 differed as to the particular form which was denoted by a 

 certain name, and as neither printed descriptions nor 

 figures can always be interpreted with certainty, it is of 

 the utmost importance that the actual specimens which 

 an author had before him when founding a species should 

 be preserved for reference in case of doubt. These 

 specimens are called type-specimens or types, and they 

 are now always preserved with the greatest care by all 

 museums which possess any, being usually marked with 

 some special label e.g., in the British Museum types are 

 indicated by a small circular green label. 



Types are of several kinds : 



If the author of a new species defines that species with 

 special reference to one particular individual, that in- 

 dividual is called the holotype of the species. 



If, while specifying a holotype, he also refers to other 

 specimens in his original description, or figures them 

 along with the holotype, these additional specimens are 

 called paratypes. 



If, however, he uses several specimens in his original 

 description without specifying one of them as the 

 holotype, these specimens are called syntypes (or 

 co-types). 



If the syntypes of a species are subsequently dis- 

 covered to belong to two or more distinct species, the 

 original author, or (with his permission, or after his 

 death) any later author, may select one of them as the 

 type of the original species : this' is called a lectotype. 

 The remaining syntypes, if not identical with other 

 species already named, may become holotypes of new 

 species at the same time. 



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