FAUNA OF THE PROVINCE OF CENTRAL EUROPE. 107 



istic of the Planorbis zone ; they were immediately succeeded in the Angulatus 

 zone by a full presentation of schlotheimian, caloceran, and vermiceran species, 

 that is, of the entire Plicatus Stock. This stock then entered upon a period of 

 decadence, slight in the-Lower Bucklandi, but more marked in the Upper Buck- 

 landi bed. Arnioceras attained its greatest development in the Upper Bucklandi 

 zone and was more persistent in the higher beds than Coroniceras. This last 

 attained its fullest expansion earlier in the Lower Bucklandi beds, and declined 

 rapidly in the Upper Bucklandi, and disappeared altogether in the Obtusus bed. 

 This decline is shown by the geratologous characteristics of the species in the 

 Upper Bucklandi beds, rather than by a less number of forms. Thus Cor. orliai- 

 latum, Gmnendense, trigonatum, and the nuilticostatus variety of bisulcatum, are all 

 degenerate species as compared with the forms of the Lower Bucklandi bed. 

 They have more convergenksided whorls, and these are usually developed at an 

 earlier age. 



Agassiceras also reached its acme in the Lower Bucklandi bed, but is more 

 persistent, and has some forms in the higher formations. Asteroceras is the only 

 series which attained its acme in the Obtusus zone, and then declined in the 

 Oxynotus zone. The oxynoticeran series reached its maximum in the Oxynotus 

 zone, and, though surviving the changes which attended migration into middle 

 liassic habitats, became extinct in that formation. 



The schlotheimian series is a highly modified series, composed of involute 

 derivatives, and ceased to exist in the Obtusus bed, but there are a few 

 dwarfed forms in the Oxynotus bed. Caloceras persisted in the highest beds, 

 whereas its highly modified derivative series, Vermiceras, is shorter lived, and 

 less fully represented in the highest beds. Arnioceras is parallel with Calo- 

 ceras, and is the radical series from which the more highly modified and 

 shorter lived Coroniceras originated. Agassiceras, the radical of the remaining 

 series, persisted from the Angulatus to the Oxynotus bed, whereas the deriva- 

 tive Asteroceras and Oxynoticeras were both shorter lived. These series, even 

 when thus minutely followed out, accord with the law of persistence in radical 

 stocks, as expressed above, on page 26. 1 Psiloceras itself is not persistent, and 

 is an apparent exception. It is the last of a long line of paleozoic secondary 

 radicals which survived in the Lower Lias. It can be compared with the 

 upper part of a stem which has reached the point of growth at which it splits' 

 into many branches. Psiloceras was in like manner resolved into derivative 

 forms, the arietian radicals Caloceras, Arnioceras, and Agassiceras. 



We have already noted and discussed the rise and progress of each series : 

 first, the radical stage, or epacme ; second, the acme; third, the final decline, or 

 paracme, caused by the prevalence of geratologous forms. The result of such a 

 serial history, when the series are considered together as one family found within 

 certain specified beds, is shown in this table. There is a precise parallelism 

 between the history of the whole and of any one series. The Planorbis and 



1 If, as we have inferred above, on page 24, the channelled and keeled species of Caloceras are transi- 

 tional to Hildoceras Walcoti and other radical forms of the Carinifera, this opinion acquires additional 

 strength, since Caloceras would then become the tertiary radical for the whole of the Carinifera of the Jura. 



