238 Mr. E. Billings on the Genus Athyris. 
diction to zoological characters.” The two genera referred to 
were Athyris and Actinoconchus. 
He specially selected T. concentrica* for the type of his genus; 
and therefore, if Spirigera be retained at all, it must be for that 
section. He refers to his ‘ Prodrome’ for a list of the species ; 
and we have thus only to examine this list in order to ascertain 
his idea of the extent of the genus. They are the following, 
taking them in the order in which they are published :— 
“8. Ceres, vultur, Circe, passer, Herculea, harpya, Hecate, tu- 
mida, concentrica, Helmersent, Puschana, decussata, plebeia, Ferro- 
nesensis, Ezquerra, Hispanica, Toreno, subconcentrica, Pelapayensis, 
Campomanensis, Mayendorfi, Roissyi, serpentina, lamellosa, am- 
bigua, Blodena, plano-sulcata, expansa, pentaédra, pectinifera, tri- 
gonella, quinquecostata, quadricostata, tricostata, and cristigalli.” 
Several of the above species do not belong to the group. This 
list shows that D’Orbigny regarded the genus: as including not 
only the types of Athyris and Spirigera, but also that of the 
genus Merista (M. Herculea), which I shall notice further on. 
I think it quite certain that, had D’Orbigny been aware that the 
genus was capable of subdivision, he would have retained Athyris 
for one of the groups which have the beak imperforate. In- 
deed, according to the laws of nomenclature, he could not have 
done otherwise with any probability of producing a permanent 
classification. 
In a valuable paper, read before the Geological Society of 
France, in May 1848, on the Brachiopoda of the Upper Silurian 
rocks of England+, Mr. Davidson made the following observa- 
tions on D’Orbigny’s genus :— 
“ Vient ensuite le genre Spirigera que le méme auteur établit pour 
les coquilles qui possédent des spires internes placées de la méme 
maniére que les Spirifer, mais qui ont des appendices et des détails 
d’organisation essentiellement différents. Ces espéces, parmi les- 
quelles nous trouvons les Terebratula, tumida, Circe, concentrica, 
subconcentrica, Roissyi, pectinifera, ambigua, Helmerseni, Pela- 
payensis, Campomanensis, Ferronesensis, Ezquerra, Hispanica, ont 
déja été distinguées par M. de Verneuil comme devant former une 
section 4 part, qu'il a nommée la section des Concentrice. Je suis 
de ’opinion de M. d’Orbigny qu’elles doivent constituer un genre. 
L’ étude minutieuse que M. Bouchard a faite de la Terebratula con- 
eentrica ne m’en laisse aucun doute; mais ce genre n’ayant pas en- 
core été convenablement caractérisé, je m’abstiendrai de l’adopter 
* “Le type est T. concentrica, De Buch. Toutes les espéces avec leur. 
synonymie se trouvent dans notre ‘Prodrome de Paléontologie strati-' 
graphique.’ ”” ; +) 
+ “ Mémoire sur les Brachiopodes du Systéme Silurien supérieur d’An- 
gleterre, par M. Th. Davidson,” Bull. Soc. Géol. Fr. v. pp, 309-314, 
