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.concentiicci^ 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 : — 



" S. Ceres, vultur, Circe, passer, Herculea, harpy a, Hecate, fu- 

 mida, concentrica, Helmerseni, Puschuna, decussata, pleheia, Ferro- 

 nesensis, Ezqiierra, Hispanica, Toreno, subconcentrica, Pelapayensis, 

 Campomatiensis, Mayendorji, Roissyi, serpentina, lamellosa, am- 

 bigua, Blodena, plano-sulcata, expansa, penta'edra, pectinifera, tri- 

 gonella, quinq^iecostata, quadricostata, tricostata, and cristigalli." 



Several of the above species do not belong to the gi*oup. 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 t, Mr. Davidson made the following observa- 

 tions on D'Orbigny's genus: — 



" Vient ensuite le genre Spirigera que le raeme auteur etablit pour 

 les coquilles qui possedent des spires internes placees de la meme 

 maniere que les Spirifer, mais qui ont des appendices et des details 

 d'orgauisation essentiellement difFerents. Ces especes, parmi les- 

 quelles nous trouvons les Terebratula, tumida, Circe, concentrica, 

 subconcentrica, Roissyi, pectinifera, ambigua, Helmerseni, Pela- 

 payensis, Campomanensis, Ferronesensis, Ezquerra, Hispanica, ont 

 deja ete distinguees par M. de Verneuil comme devant former une 

 section a part, qu'il a nommee la section des Concentricce. Je suis 

 de Fopinion de M. d'Orbigny qu'elles doivent constituer un genre. 

 L' etude miuutieuse que ]M. Bouchard a faite de la Terebratula con- 

 ce7itrica ne m'en laisse aucun doute ; mais ce genre n'ayant pas en- 

 core ete convenablement caracterise, je m'abstiendrai de I'adopter 



* " Le type est T. concentrica, De Buch. Toutes les especes avec leur 

 synonymic se trouvent dans notre ' Prodrome de Paleontologie strati- 

 graphique.' " 



t " Memoire sur les Brachiopodes du Systeme Silurien superieur d'An- 

 gleterre, par M. Tli. Davidson," Bull. See. Ge'ol. Fr. v. pp. 309-314. 



