Zoology uniform and permanent. 265 



names is so defined as to be less extensive in signification than the earlier, for 

 if the later includes the type of the earlier genus, it would be cancelled by 

 the operation of § 4 ; and if it does not include that type, it is in fact a distinct 

 genus.] 



But when the later name is more extensive than the earlier, the following 

 rule comes into operation : — 



\_A later name equivalent to several earlier ones is to be cancelled.] 



The same principle which is involved in § 6, will apply to § 8. 



§ 8. If the later name be so defined as to be equal in extent to two 

 or more previously published genera, it must be cancelled in toto. 



Example. — Psarocolius, Wagl. 1827, is equivalent to five or six genera 

 previously published under other names, therefore Psarocolius should be 

 cancelled. 



If these previously published genera be separately adopted (as is the case 

 with the equivalents of Psarocolius), their original names will of course pre- 

 vail ; but if we follow the later author in combining them into one, the fol- 

 lowing rule is necessary : — 



\_A genus compounded of two or more previously proposed genera whose cha- 

 racters are now deemed insufficient, should retain the name of one of them.'] 



It sometimes happens that the progress of science requires two or more 

 genera, founded on insufficient or erroneous characters, to be combined to- 

 gether into one. In such cases the law of priority forbids us to cancel all 

 the original names and impose a new one on this compound genus. We must 

 therefore select some one species as a type or example, and give the generic 

 name which it formerly bore to the whole group now formed. If these ori- 

 ginal generic names differ in date, the oldest one should be the one adopted. 



§ 9. In compounding a genus out of several smaller ones, the earli- 

 est of them, if otherwise unobjectionable, should be selected, and its 

 former generic name be extended over the new genus so compounded. 



Example. — The genera Accentor and Prunella of Vieillot not being con- 

 sidered sufficiently distinct in character, are now united under the general 

 name of Accentor, that being the earliest. So also Cerithium and Potamides, 

 which were long considered distinct, are now united, and the latter name 

 merges into the former. 



We now proceed to point out those few cases which form exceptions to 

 the law of priority, and in which it becomes both justifiable and necessary to 

 alter the names originally imposed by authors. 



\_A name should be changed ivhen previously applied to another group which 



still retains it.] 



It being essential to the binomial method to indicate objects in natural 

 history by means of two words only, without the aid of any further designa- 

 tion, it follows that a generic name should only have one meaning, in other 

 words, that two genera should never bear the same name. For a similar 

 reason, no two species in the same genus should bear the same name. When 

 these cases occur, the later of the two duplicate names should be cancelled, 

 and a new term, or the earliest synonym, if there be any, substituted. When 

 it is necessary to form new words for this purpose, it is desirable to make 

 them bear some analogy to those which they are destined to supersede, as 

 where the genus of birds, Plectorhynchus, being preoccupied in Ichthyology, 



