E. Billings on the Genus Athyris. 57 
will not have any effect. All that can be done is to rectify; 
not to destroy. One of the exceptions to this rule is thus ex- 
ressed in No. 11. ‘A name may be changed when it implies 
a false proposition which is likely to propagate important errors.” 
According to this exception if the name Athyris should be 
applied to the JS. concentrica group there is a possibility of its 
falling into the list of synonyms; for, although no very impor- 
tant error would be superinduced, yet few naturalists can apply 
it to shells with a well defined foramen without feeling that such 
an application is to some extent, inconsistent with the purity of 
scientific nomenclature. 
3.—A generic name, when once established, should never be can- 
celled in any subsequent subdivision of the group, but retained in a re- 
stricted sense for one of the constituent portions.” 
“4A generic name should always be retained for that portion of 
the original genus which was considered typical by the author.” 
_ This latter rule is preceded by some introductory observa- 
tions which should be embodied in it as they in fact form a 
part of the rule itself. They are especially applicable to this 
case. 
nyms, will also often serve to point out the particular species which by 
implication must be regarded as the original type of the genus. In suel 
cases we are justified in restoring the name of the old genus to its typl- 
cal 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 p. 
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, nor with McCoy’s generic description, nor with 
his typical figure. Therefore it cannot be arbitrarily selected as 
the type, and the name Afthyris, in consequence, retained for 
that group. I 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 
Investigati . ete 
In this instance, as before mentioned, McCoy was prep 
& work exclusively devoted to Carboniferous fossils, am 
AM. Jour. Scr.—Sxconp SEertss, VoL. XLIV, No. 130.—Juxy, 1867. — 
8 
