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 146, 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 supposing 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 this 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 further 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 synonynis. 
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. Foss. 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 perforated 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 ‘ Paléontologie Francaise,’ vol. iy. 
p. 357, he says :—‘ This division has already two generic names 
which we cannot preserve, because they are in complete contra- 
