NOMENCLATURE. 95 



species referred to the primitive group by its author at the time when it was de- 

 scribed, or when he enumerated the species contained in it." 



The rule that a subsequent author can not revise a genus and substitute as 

 its type a species different from that relied upon by the founder of the genus seems 

 to be well settled in England and America. The instances of strictly adhering to 

 it under circumstances where it would have seemed to accommodate the author to 

 violate it, are numerous. For instance, Professor Hall, mistaking the type of the 

 genus Retzia, proposed and defined the genus Rhynchospira ; afterward ascertain- 

 ing that Rhynchospira was a synonym for Retzia, he abandoned it and proposed 

 Rhynchotreta for the form which he had originally mistaken for Retzia. Had it 

 not been for this rule he might have abandoned Retzia evax as the type of his genus 

 Rhynchospira, and substituted Rhynchondla cuneata, which became the type of 

 Rhynchotreta. If you can substitute another than the original species as the type of 

 a genus, I can substitute another, and so we destroy o\\ fixity in the type and desig- 

 nated characters, throw the science into confusion, and seriously impair the value 

 and reliability of generic characters. 



When an author has specified no type, the first species defined is to be taken 

 as the type, or if the genus is to be divided, no type having yet been selected, a 

 species may be chosen from among those originally specified as belonging to the 

 genus, due regard being paid to the necessity of retaining as many of the original 

 species as possible in the division which is to retain the old name. 



In dividing a genus of which there are already synonyms, if the synonyms are 

 typified by the same species or group of species selected as types of the primitive 

 genus, they should not be again used. When, however, the so-called synonyms are 

 founded on species belonging to different sections of the genus, although the names 

 may have been considered coextensive in their application, and the genus is to be 

 divided accordingly, the so-called synonyms become the proper designations for 

 which other names can not be applied. 



In case of the consolidation of two or more groups of the same nature, the 

 oldest name must be retained for the whole. If both, or all, are of the same 

 date, the reviser may select the one to be retained. If a name be so defined as 

 to be equal in extent to two or more previously described, it must be canceled. 

 When it is necessary to divide a species, the form which received the old specific 

 name must retain it. 



A generic name must have a single meaning, and therefore two genera can not 

 bear the same name, even though belonging to distinct subkingdoms. 



AS TO PUBLICATION. 



Publication consists of the insertion of a distinct exposition of essential char- 

 acters in a printed book which is kept for sale, or which has been generally dis- 

 tributed among those conversant with the subject. Where figures are necessary to 

 an understanding of the character of the organism, they must accompany the defi- 

 nition or it will be invalid. The tendency of the science of palaeontology is to de- 

 mand in all cases both definition and illustration before the publication is to be 

 recognized. There are many species whose characters are so complicated and parts 

 so minute, that an exposition of the essential ones, so they may be understood by 

 those conversant with the fossils in the class, can only be made by illustration 



