INSTITUTE OF SCIENCE, PHILADELPHIA. 561 



NOTES ON NOMENCLATURE. 



In 1877 the writer reported to the American Association for the Advance- 

 ment of Science on the state of opinion among American men of science in re- 

 gard to the matter of Rules for settling questions of nomenclature in Zoology 

 and Botany. Since then he has added a good deal to his experience in ques- 

 tions of nomenclature, and concludes that a statement of the principles upon 

 which points of nomenclature have been settled in this memoir may be of use 

 to students who have to use it. The subject is one upon which opinions 

 change with experience. Conclusions which seem axiomatic with the begin- 

 ner are questioned more or less seriously, or even rejected, by the maturer 

 student. With the more minute study of groups names have greatly multi- 

 plied, and it daily becomes more necessary to adhere to some fixed standard. 

 Those familiar with the history of the subject know that the earlier naturalists 

 had no clear conception of the importance of a fixed nomenclature, that the 

 idea has grown in comparatively modern times, and that different branches of 

 Zoology have developed their nomenclature with some differences of detail, 

 which the writer believes it best to recognize, without insisting on an abso- 

 lutely common standard in all details. Such differences are those exhibited 

 in the literature of Gall-insects, Microlepidoptera, Echinoderms and modern 

 Botany. 



The following notes may, therefore, be understood as intended to apply 

 strictly to the literature of Mollusca, though very largely applicable to all 

 bumches of Zoology, and to represent the results of a somewhat wide experi- 

 ence in that field. 



The occasion for scientific nomenclature is the necessity of having a sin- 

 gle fixed name for a zoological entity, which will have a single fixed meaning 

 when used, without reference to the language or nationality of the user. The 

 idea involved \s fixity of the name, and, therefore, its availability for world-wide 

 use among scientific men. Our first and fundamental rule, therefore, must 

 be: 



I. The object of nomenclature is the fixity of scientific names. 



To this it necessarily follows that whatever disturbs the fixity of a name 

 which is entitled to be used, is opposed to the fundamental principle of nomen- 

 clature, and the burden of establishing his right to disturb rests upon the dis- 

 turber. 



Our second rule or axiom of nomenclature is : 



II. Other things being equal, the prior name is entitled to precedence. 



This is universally admitted, and all the other rules of nomenclature have 



