Mr. E. Billings on the Genus Athyris. 243 
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 otherwise.”’ 
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. twmida 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 
