i 
REMARKS. 85 
Ly: 
GEOLOGICAL AND FAUNAL RELATIONS. 
REMARKS. 
HE point of view in this chapter naturally rests upon the assumed existence 
of a persistent series of discoidal shells which formed a continuous radical 
stock for all the Ammonoidea, beginning in the Silurian and having their last 
representative in Psiloceras of the Planorbis bed. This, as we have said above, 
was closely allied to Gymnites of the Trias, and enables us to connect all the 
Ammonitine of the Jura directly with the more ancient primary radicals of 
the central trunk of the genealogical tree. The chronological distribution of this 
trunk of forms must be actually represented by more or less broken lines, until 
all the gaps now existing between the different systems or periods in the earth’s 
history have been filled by the progress of discovery. 
The surviving genus of the trunk stock, Psioceras, consists of a series of spe- 
cies which we have called the Radical Stock of the Arietidse, which became in 
the Lower Lias the generator of new series of peculiar modifications, spreading 
out from Psi. caliphyllum or planorbe like the spokes of a fan, each genetic radius 
being composed of a separate series of modifications or species. We have given 
this classification above, and shown that the chronological distribution of the 
species in each series is in accord with their positions ‘in the series; it now 
remains to apply the same classification to the solution of the problems of choro- 
logical distribution, 
There are many more or less complete lists and monographs of local faunas 
in the province of Central Europe, and extensive collections, which afford a solid 
basis for comparison. The preliminary work of Prof. Jules Marcou,' in synchro- 
nizing the minuter subdivisions of the Jura in Central Europe, was completed 
by the more extensive application of the same principles by Oppel,” who visited, 
studied, and synchronized the faunas of the different localities, and identified the 
same beds in a large part of this province. The illustrated publications of Hauer,’ 
Neumayr,' Wiihner,> Geyer,’ and Herbich,’ have also thrown a strong light upon 
the peculiarities of the faunas of the eastern part of Europe, particularly the 
basin of the Northeastern Alps. All of these researches, and many others not 
mentioned, have made still further advances in the classification of the chrono- 
logical relations of the minuter subdivisions or beds practicable. 
1 Roches des Jura, pp. 23, 162, 173, et seq. 
2 Die Jura-Format. Eng. Frankr. u. d. siidwestl. Deutschl. Wiirtt. Jahresb., XII. - XIV., 1856. 
3 Die Cephal. a. d. Lias d. nordostl. Alpen, Denksch. Akad. d. Wissensch., Wien, XI. 
4 See note 2, page 86. 5 Mojsis. et Neum., Beitr., II. - VI. 
6 Ceph. heirl. Schich, Abh. k. k. geol. Reichsans., XII. 
7 Das Széklerland, Mitt. Jahrb. d. k. ungar. Anst., V., Pt. IT. 
