48 TYPE AMMONITES— IV Aug. 



if he works methodically, bring the number of plates, which it is 

 necessary for him to consult, within quite reasonable limits. 



Another method presents itself — the stratigraphical. The student 

 has possibly a shrewd idea as to the formation from which his specimen 

 has been obtained. He should then look for the genera which have 

 been figured from that formation. For his help in this search there 

 was given in the Appendix to Vol. II, p. c, a Chronological Analysis 

 of the genera illustrated in those two volumes : now there is given a 

 similar analysis of the genera figured in Vols. Ill, IV. The translation 

 of the chronological terms into the ordinary formation names, or vice 

 versa, may be learnt from Table I of Vol. IV (pp. 6-13). The student 

 using these two methods should quickly and easily find what he seeks, 

 if it is figured in these volumes ; but he may find nothing like his speci- 

 men ; because it has to be remembered that among the rich fauna of 

 Jurassic Ammonites there are yet many series untouched in these volumes. 



Chronological Analysis — II 



(Pis. CXXXI — CDXXII. Genera in approximate chronological 

 order — late to early — in each Age. . See Vol. II, App. p. c.) 



Ages Genera 



GiGANTiTAN : Glottoptychinites, Titanites, Briareites, Gigantites, 



Galbanites, Trophonites. 

 Behemothan : Crendonites, Simotoichites, Leucopetrites, Glauco- 



lithites. Behemoth. 

 Paravirgatitan : Lydistratites, Paravirgatites, Pectinatites, Wheat- 



leyites. 

 Prionodoceratan : Prionodoceras, Dichotomoceras. 

 RiNGSTEADiAN : Ringsteadia. 

 Perisphinctean : Perisphinctes. 

 Cardioceratan : Vertebriceras, Anacardioceras, Kranaosphinctes, 



Goliathiceras, Chalcedoniceras, Sagitticeras, Korythoceras, 



Miticardioceras, Klematosphinctes, Neumayriceras, Hortoniceras. 

 Vertumniceratan : Pavloviceras, Alligaticeras, Pocuhsphinctes, Putea- 



liceras, Aspidoceras, Sutherlandiceras, Eboraciceras, Bourke- 



lamberticeras. 

 Kosmoceratan : Longgeviceras, Trinisphinctes, Binatisphinctes, Hamuli- 



sphinctes, Rursiceras, Weissermeliceras, Zugokosmokeras, Guliel- 



mites, Gulielmiceras. 

 Proplanulitan : Galilaeanus, Sigaloceras, Crassiplanulites, Galilaeites, 



Galilaeiceras, Cadoceras, Proplanulites, Gowericeras, Toricellites. 

 Macrocephalitan : Pleurocephalites, Tmetokephahtes, Macrocephalites, 



Macrocephaliceras, Toricelliceras, Kepplerites, Catasigaloceras, Ana- 



planulites, Catacephalites, Dohkephalites, Kamptokephahtes, 



Homoeoplanulites, Cerericeras. 

 Oxyceritan : Suspensites. 

 TuLiTAN : Morrisiceras, Tuhtes, Bullatimorphites, Morrisites, Tulo- 



phorites, Madarites, Rugiferites, Pleurophorites, Sphseromorphites. 

 Gracilisphinctean : GraciHsphinctes. 

 ZiGZAGiCERATAN : Zigzagites, Parkinsonites, Zigzagiceras, Procerites, 



Ebrayiceras, Polysphinctites, Planisphinctes, Patemorphoceras. 

 Parkinsonian : Haselburgites, CEcoptychoceras, Phanerosphinctes, 



Polystephanus, Stegeostephanus, Dimorphinites ^'ermisphinctes, 



Prorsisphinctes, Stomphosphinctes, Diplesioceras, Parkinsonia, 



Garantiana. 



