Mr. E. Billings on the Genus Athyris. 2-13 



part of the rule itself. They are especially applicable to this 

 case. 



" When a genus is subdivided into other genera, the original name 

 should be retained for that portion of it as at first defined. Authors 

 frequently indicate this by selecting some one species as a fixed point 

 of reference, which they term the * type of the genus.' When they 

 omit doing so, it may still in many cases be justly inferred that the 

 first species mentioned on the list, if found accurately to agree with 

 their definition, was regarded by them as the type. A specific 

 name, or its synonyms, will also often serve to point out the parti- 

 cular species which by implication must be regarded as the original 

 type of the genus. In such cases we are justified in restoring the 

 name of the old genus to its typical signification, even when later 

 authors have done othervdse." 



Now this rule bears directly on the question, because many 

 naturalists are under the impression that the first species placed 

 on the list must necessarily be regarded as the type where the 

 author is silent on that point. But, according to the above (and 

 common sense), it is only so if found accurately to agree with the 

 definition. Spirigera concentrica does not agree either with the 

 name Athyris, or with M'Coy^s generic description, or with 

 his typical figure. Therefore it cannot be arbitrarily selected 

 as the type, and the name Athyris, in consequence, retained for 

 that group. Indeed in many instances it would be impossible 

 that the first species placed in the genus should be the type; for 

 the author might not have the true type in the collection under 

 investigation. 



In this instance, as before mentioned, M^Coy was preparing 

 a work exclusively devoted to Carboniferous fossils, among 

 which A. tumida does not occur. In preparing his description 

 of the genus he may, however, have had that species before him, 

 and its imperforate beak may have had some influence. 



" § 5. When the evidence as to the original type is not clear and 

 indisputable, then the person who first subdivides the genus may 

 affix the original name to any portion of it at his discretion ; and no 

 later author has a right to transfer that name to any other part of 

 the original genus." 



This last paragraph applies as well to the author who first 

 subdivided the genus as to others. Once a genus is established 

 or subdivided, on sound principles, it becomes the property of 

 science, and the author himself (either of the genus or the sub- 

 division) can make no change. He may amend, by striking out 

 the errors, if any there be, but all that is true must remain. 



I think that, on a careful study of all the circumstances, it 

 will be perceived that Mr. Davidson^s first adjustment of this 



