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, 

 ]844<, Spiriyera, D'Orbigny, 1847. Each 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. Cleiothyris 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. tumida, Dal., or lierculea, Bar- 

 rande," and specially named them as the types. 



He retained Spiriyera 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 ari'angement. In a note he states, " Before 

 coming to the above conclusion, I 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 palaeontologists " {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 ete critique par plusieurs naturalistes qui 

 ont insiste sur ce que le terme Athyris avait ete originairement et positive- 

 ment applique par son auteur a la T. concentrica et sur Timproprie'te de 

 I'autre denomination pour designer des coquilles telles que les T. tumida, 

 Herculea, &c. M. Suess nous a informe' {Neues Jahrbuch, p. 62, Janvier 



