1923 CHRONOLOGY 49 



Stepheoceil\tan : Hlawiceras, Pseudobigotella, Rhabdodites, Cado- 

 moceras, Strenoceras, Leptosphinctes, Caumontisphinctes, Spha^r- 

 oceras, Nannolytoceras, Teloceras, Chondroceras, Epabdtes, Mascke- 

 ites, Stepheoceras. 



SoNNiNiAN : Kallistephanus, Rhytostephanus, (Ecostephanus, Skirr- 

 oceras, Skolekostephanus, Otoites, Papilliceras, Sonninia, Ambly- 

 oxyites, Labyrinthoceras, Kumatostephanus, Frogdenites, Witchellia, 

 Emileia, Lissoceras, Mollistephanus, Stiphromorphites, Pelekodites, 

 Zugophorites, Sherbornites, Fissilobiceras, Trilobiticeras, Docid- 

 oceras, Graphoceras, Kleistoxyites, Eudmetoceras, Euaptetoceras. 



LuDWiGiAN : Abbasites, Ambersites, Planammatoceras, Manselia, 

 Eiycites. 



DuMORTiERiAN : Xeinophylloceras. 



Grammoceratan : Pachammatoceras, Hammatoceras. Phlyseogram- 

 moceras, Esericeras. 



Haugian : Thysanoceras, Catacoeloceras, Phymatoceras, Pelecoceras. 



HiLDOCERATAN I Planulites, Frechiella, Hildoceratoides. 



Harpoceratan : Hildaites, Dactylioceras, Pseudolioceras, Porpoceras, 

 Murleyiceras, Paltarpites. 



Amaltheian : Paltopleuroceras, Argutarpites, Amauroceras. 



Liparoceratan : Beaniceras. 



PoLYMORPHiTAN : Tiagophylloceras, Kallilytoceras, Coeloceras, 

 Jamesonites, Phricodoceras. 



Deroceratan : Apoderoceras, Cnicilobiceras. 



OxYNOTicERATAN : Fastigiceras, Victoriceras, Tutchericeras, Oxyno- 

 ticeras, Retenticeras. 



AsTEROCERATAN : Aiietites. 



CoRONiCERATAN : AgcLSsiceras, Aetomoceras, Ammonites. 



Caloceratan : Schlotheimia, Caloceras, Psiloceras. 



To attempt the identification of an Ammonite without first making 

 observations as to its characters, the nature of its venter, of its rib-curve, 

 of its ribbing, and most especially of its suture-hne, is only to court 

 disaster. Nor should the student venture to give to a specimen from 

 one formation the name of a species from another formation, even though, 

 locally, he may find the two formations in contact, and may therefore 

 think that the time-interv^al between them is only a ver>^ short one : 

 this will be certain to bring trouble. Those who hghtly say " this species 

 may or must have hved on longer in our area than in others " should 

 first reflect on the extraordinary palaeo-geographical comphcations which 

 would ensue if their words were correct, as well as on the fact that zonal 

 work — the identification of the position of strata by means of Ammonites 

 — ^w^ould be worthless. There are many cases of the repetition of hke 

 forms (heterochronous homoeomorphy) which may easily mislead those 

 who do not proceed with caution and examine minutely, especially for 

 internal characters. To explain by an airy phrase, without due know- 

 ledge of facts and without mature consideration of the consequences 

 involved, is a serious fault — unhappily, far too common in geological work. 



A particularly unfortunate example of the danger of extending the 

 range of Ammonites — of identif}ing the species of one formation %vith 

 those of another — is shown in the recently-pubhshed work of Marcel 

 Lissajous (Faune Bathonien de Macon ; Lab. Geol. de Lyon, III, 1923). 

 He identifies certain Bathonian species from his zone of arhiistigerum 

 with species which I named from the zigzag bed of the Inferior OoHte. 

 Now the arhiistigerum zone is the equivalent of the Great Oohte of 



