Hyatt.] 
24 
fMay 16, 
Planorbis zone containing Psiloceras alone has not yet been demon- 
strated in the Northeastern Alps, though such a fauna exists in 
South Germany. Nevertheless the evidences palseozoologically are 
so complete, that I feel disposed to support the opinion that the four 
series of the Arietidse above mentioned were derived by choro- 
logical migration from the Northeastern Alps. 
This conclusion must be true, or else the separate and distinct 
origin of the faunas of South Germany and the Northeastern Alps 
and perhaps others like that of England will have to be admitted. 
It is very difficult, if this last theory be accepted, to account for 
the phenomena subsequently occurring in the residual faunas. 
The residual faunas show that the radical types of series are apt to 
occur later in them than in those that have been called autochtho- 
nous. The greater completeness of the earlier faunas of the North- 
east Alps in radical forms and series also coincides with the similar 
completeness observed subsequently in the basins of South Ger- 
mamr and Cote D’Or in the forms of the progressive series, which 
alone appear to have arisen there. Thus in basins where forms and 
series must have arisen according to the evidence afforded by the 
earlier appearance of radical species, there are, as a rule, larger 
numbers of species and varieties than in those which do not possess 
radical species, or in which the}^ appear later in time. The hy- 
pothesis of the independent origin of series in these two principal 
autochthonous basins, would also involve the corollary that pre- 
cisely parallel series and identical species connected by similar va- 
rieties could also be independently evolved in these different ba- 
sins. The English basin also possesses very complete series and 
like South Germany has a bed exclusively occupied by Psil. plan- 
orbe but the absence of peculiar forms, and the later incoming of 
radical species of other series, show that the hypothesis of the in- 
dependent origin of similar species or polygenesis cannot be ad- 
mitted without more evidence than is now in our possession. The 
future completion of the geological evidences by the discovery of 
still more complete series in the Planorbis, and later Triassic of 
the Northeastern Alps seems, therefore, to be likely since, as we 
have said above, the unexampled profusion of the Triassic fauna 
and the progress of recent discoveries point also to the same re- 
sult. It seems preferable to adopt this conclusion as presenting 
the least difficulties. The view, that South German}^ might have 
been the basin in which the radical stock and all the radical series 
