THE RULES OF NOMENCLATURE 363 



Sowerby, of which name Lutraria livata J. Sowerby is a 

 synonym.* 



The fate of all specific homonyms is not quite so clear, 

 because of the possibility that they may be transferred to 

 other genera. Thus of the two species named Spirifer 

 pinguis, Sowerby's is now Bvachythyvis pinguis, and 

 Zieten's is Spiriferina pinguis : there can therefore be 

 no danger of confusion between them, and both trivial 

 names may be kept. It is true that the International 

 Congress has a very drastic rule " Once a homonym, 

 always a synonym," meaning that once a name is 

 suppressed on account of homonymity it can never be 

 revived, even on transference to another genus; but 

 while this applies quite clearly to cases where the homo- 

 nym has had a new name substituted for it while it was 

 still in its original genus, it is not clear that it applies to 

 cases where the homonymity was overlooked until the 

 change of genus was made, as in the case of Spiriferina 

 pinguis. 



One more exception to the law of priority must be 

 noted. It has been found impracticable to insist on its 

 covering both Animal and Vegetable Kingdoms simul- 

 taneously, so botanists and zoologists have agreed, while 

 each accepting it within his own kingdom, to let the 

 nomenclature of the two be quite independent. Thus 

 Zeilleria is the name both of a Carboniferous pterido- 

 sperm leaf, and of a Jurassic brachiopod. No practical 

 confusion is likely to arise between the two. 



These are the only valid exceptions to the law of 

 priority. There are one or two other exceptions that 

 have been proposed but are now quite rightly rejected. 

 In the first place a name must not be rejected because it 



* It must be clearly understood that the term synonym implies 

 two names for one thing, while homonym implies the same name for two 

 things. 



