244 Mr. E. Billings on the Genus Athyiis. 



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 M. 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 

 makivg it exactly of the same extent, the latter name should be 

 cancelled in 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 original 

 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 ths 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 P. Boemer, in the third 

 edition of Bronu's * Lethsea Geognostica,' adopted Davidson's 

 classification, and copied his diagnosis of both genera in full. 

 They cited A. tumida as the type oi Athyris. ''Die typische 

 Art ist Athyris tumida, M'Coy {At^-ypa tumida, Dalman). An- 

 dere Arten sind A. Herculea {Terehratula Herculea, Barrande), 



