Mr. E. Billings on the Genus Athyris. 237 



that such a collection as he was then engaged upon would con- 

 tain one or more specimens. 



If we take the paragraph No. 3 as a part of the generic 

 description^ then A. tumida is included. If, on the other hand, 

 we confine ourselves to the extract from page 1-16, it is not ex- 

 cluded, as there is no reference made there to the structure of 

 the beak. This latter diagnosis is sufficiently comprehensive and 

 general in its terms to include Athyris, Spirigera, and Merista. 

 He did not place A. tumida in the genus, for the reason that his 

 work was confined altogether to the Carboniferous fossils, among 

 which it does not occur. But he did so afterwards, when he 

 described Professor Sedgwick's Silurian fossils, as will be shown 

 further on. He was wrong in sujjposing that all the species 

 were imperforate — a matter of little consequence, as it was sim- 

 ply an error of observation, which does not vitiate. Had the 

 genus turned out to be not capable of subdivision, all that could 

 be done now with tliis error would be to strike it out. There 

 was sufficient in his diagnosis to indicate what group of fossils 

 was intended. He was also wrong in supposing S. concentrica 

 to be a Carboniferous fossil : it is Devonian. It may be that he 

 mistook some other species with an imperforate beak for that. 

 It will be seen farther on that Prof. King made a similar mis- 

 take with respect to this very species, having taken T. scalprum, 

 Barrande, for it — an error which was detected by Mr. Davidson. 

 Altogether he referred eleven species to the genus, several of 

 which have been shown to be synonyms. 



In the same work he proposed another genus, Actinoconchus; 

 but as it was founded on error, he afterwards withdrew it, and 

 added it to Athyris (Brit. Pal. Poss. p. 436), All scientific works 

 abound more or less with such misconceptions. 



That the genus was understood by other naturalists to include 

 A. tumida is proved by the following facts. It is well known 

 that the genus Spirigera was proposed by D'Orbigny, in 1847, 

 simply as a substitute for Athyris, on the ground that this 

 latter name implies the absence of a foramen, and is therefore 

 not appropriate for species with a pei-forated beak. It is quite 

 clear that D'Orbigny considered his genus to be precisely the 

 same in extent as Athyris. All the species, therefore, which 

 he placed in Spirigera he regarded as fairly within the group ; 

 and it is unquestionable that he would have referred them all 

 to Athyris had not that name appeared to him objectionable. 

 I have not seen his original description in the ' Annales des 

 Sciences Naturelles,' referred to by Mr. Davidson in the ex- 

 tract given below ; but in the ' Paleontologie Pran9aise,' vol. iv. 

 p. 357, he says : — "This division has already two generic names 

 which we cannot preserve, because they are in complete contra- 



