Mr. E. Billings on the Genus Athyris. 241 
2. Subdivision of the Genus by Mr. Davidson in 1854. 
From all the facts above given it may be gleaned that in 1853, 
when Mr. Davidson was engaged in the preparation of his 
‘General Introduction,’ this group of Brachiopoda was known 
as a single genus, but with two generic names—Athyris, M‘Coy, 
1844, Spiriygera, D’Orbigny, 1847. Hach of these was intended 
by its author to include the whole group. M/‘Coy was under 
the impression that all the species had the beak imperforate, 
while D’Orbigny maintained that they were all perforated. 
Both authors were partly wrong and partly right. The genus 
was capable of subdivision; but no one had as yet undertaken 
that task, unless, indeed, the observations of Prof. King and 
Suess can be so construed. With regard to the latter, as the 
genus Merista is now well understood and is different from 
Athyris, it does not affect the question. Cletothyris may be 
regarded as obsolete. 
Mr. Davidson, in his ‘ General Introduction,’ in endeavouring 
to reconcile the conflicting nomenclatures of D’Orbigny and 
M‘Coy, divided the genus, retaining the name Athyris for 
“forms with an apparently imperforate beak or closed foramen, 
variously disposed septa, and largely developed dental plates.” 
He selected two species, “ A. twmida, Dal., or Herculea, Bar- 
rande,” and specially named them as the types. 
He retained Spirigera for the group of which S. concentrica is 
the type. As to this latter group, by whatever name it may be 
hereafter known, its extent will most probably always be that 
assigned to it in the work in question. 
The genus Athyris, however, as there defined, included Merista 
—a circumstance which, however, as I[ shall presently show, in 
no way vitiates the arrangement. In a note he states, “ Before 
coming to the above conclusion, [ submitted my views to Mr. 
Deshayes, Mr. Salter, and others, who seemed to consider that 
this mode of compromising the difficulty could not reasonably 
be objected to by the two authors principally concerned, nor by 
the generality of paleontologists” (op. cit. p. 86). 
Afterwards this classification was strongly objected to by 
several naturalists, who maintained that M‘Coy had “ originally 
and positively ” applied the name Athyris to the S. concentrica 
group, and therefore it could not be transferred to the other 
principal section. He, therefore, in the French edition of this 
introduction (1856), abandoned his first arrangement *, and 
* “Mais ce moyen terme a été critiqué par plusieurs naturalistes qui 
ont insisté sur ce que le terme Athyris avait été originairement et positive- 
ment appliqué par son auteur a la T. concentrica et sur l’impropriété de 
Vautre dénomination pour désigner des coquilles telles que les T. tumida, 
Herculea, &e. M. Suess nous a informé (Neues Jahrbuch, p. 62, Janvier 
