244, Mr. E. Billings on the Genus Athyris. 
question was the most wise, the best for the interests of science, 
and the most just towards all the parties concerned that could 
be devised. It was not inconsistent with the laws of nomen- 
clature, but in perfect accordance with them in every particular, 
and therefore should be retained. 
In one respect, however, it has been modified. <Athyris, as 
first defined by him, included Merista of Prof. Suess. This was, 
no doubt, due to the fact that the characters of this last-named 
genus were not then accurately known to the scientific public. 
This makes little difference. Merista has long since been sepa- 
rated, with its type WM. Herculea, leaving the other and most 
important group for Athyris, with A. tumida for the type. 
With regard to Spirigera, I think it can also be retained, not- 
withstanding the following rule :— 
““§ When two authors define and name the same genus, both 
making it exactly of the same extent, the latter name should be 
cancelled zn toto, and not retained in a modified sense.”’ 
If the name Athyris had been extremely objectionable, accord- 
ing to the 11th rule, Spirigera might have cancelled it alto- 
gether. But the true principle of interpreting these laws is, 
that where there is any possibility at all of saving the origimal 
name, it must be saved, even if the rules be strained to their 
utmost in that direction. The rules cannot be stretched to de- 
stroy, but they may be strongly bent in the other direction, to 
preserve. If a generic name should be appropriate for a large 
number of the species of the group to which it was originally 
applied, and not very objectionable as to a few only, I doubt whe- 
ther it can be changed. Such was the case with Athyris when 
D’Orbigny objected to it. More than two-thirds of the species 
designated by him are imperforate, and he should have retained 
the name for these. Some naturalists were therefore in favour. 
of rejecting Spirigera altogether, others of retaining it. It is 
not, therefore, a case clearly within the rule; and as there was 
much doubt, the best course to take, as soon as it was found 
possible to do so, was taken by Mr. Davidson. He decided in 
favour of preserving the name. 
3. Authors who have adopted the Classification. 
In 1856, Professors H. G. Bronn and F. Roemer, in the third 
edition of Bronn’s ‘ Lethza Geognostica,’ adopted Davidson’s 
classification, and copied his diagnosis of both genera in full. 
They cited A. twmida as the type of Athyris. ‘ Die typische 
Art ist Athyris tumida, M‘Coy (Atrypa tumida, Dalman). An- 
dere Arten sind 4. Herculea (Terebratula Herculea, Barrande), 
ui SMe i PUES i 0b La 
