REMARKS. 



IV. 

 LOGICAL AND FAUNA! RELATIONS 



lil If \KKS. 



THE ]><>int of view in tlii~ chapter naturally rests upon the assumed existence 

 persistent discoidal shells which formed a continuous radical 



ill the Ammonoidea, beginning in tin- Silurian and having their last 



i tentative in Psil< ras of the Planorbis bed This, as we have said above, 



loselv allied to Gymnites of the Trias, and enables us to connect all the 



Ainmonitina <>|' the Jura directly with the more ancienl primarj rad cals <«f 



the central trunk of the genealogical tree. The chronological distribution of this 



trunk of forms must be actually represented by more <>r !<■-> broken lines, until 



nil the gaps now existing between the different systems <>r periods in the earth's 



v have been filled by the progress of discovery. 



The surviving genus of the trunk Btock, /' onsists of :i Beries of Bpe- 



rhich we have called the Radical Stock of the ArietidsB, which became in 



the L of peculiar modifications, spreading 



out from /'■•''. caKphyUum or pbmorbe like the -pukes of a fan, each genetic radius 



composed of a separate Beries of modifications or Bpecies We have given 



■ ml Bhown that the chronological distribution of the 



- in each in accord with their positions in the series; it now 



i- to apply tin- same classification to the solution of the problems of choro- 



:1 distribution. 



There are many mure or less complete lists and monographs of local faunas 



in the proi ' ntral Europe, and extensi\ Ilections, which afford a >• >1 i<l 



The preliminary work of Prof Jules Marcou, 1 in synchro- 



the minuter subdivisions of the Jura in Central Europe, was completed 



l>_v the more extensive application of the same principles bj Oppel, 1 who visited, 



studied, and synchronised the faunas of the different localities, and identified the 



Mine beds in al of this pnn ii , The illustrated publications of Hauer, 1 



Neumayr/ Wal G nd Herbich/ have also thrown a strong light upon 



the peculiarities of the faunas <,f the eastern part of Europe, particularly the 



Alps All of these researches, and many othei 

 mentioned, have made still further advances in the classification of the chrono- 

 : the minuter subdi i beds practicable. 



» M ll \ l 



\ll 

 Jahrb .1 k II 



