Hyat,t.] 
30 
[May 16, 
have said above, contain forms which show that they were estab- 
lished later in time than those of the basins of South Germany, or 
Cote d’Or. 
M. Dieulefait’s observations also accord with my opinion, that 
the faunas of the south German basin during the time of the depo- 
sition of the Bucklandi bed made a return migration to the east, peo- 
pling the Northeastern Alps basin with progressive forms first, and 
then spread to the south and west into Italy. It would be difficult 
to account for the absence of the upper beds of the Lower Lias in 
the Mediterranean part of Provence or for the mixed character of 
the faunas of these same beds in Italy upon any other theory than 
direct connection with the similar faunas of the Northeastern Alps 
in the east and a corresponding isolation from the faunas of Central 
Europe to the west. 
I am well aware of the great difficulties under which one labors 
in writing an article of this kind so far away from the localities in 
which the phenomena have been and are still continually being ob- 
served. The large amount of negative evidence which has to be 
taken into consideration in all the countries to the south and north 
of the autochthonous zone of the Arietidse will also rightfully create 
doubt in the minds of specialists. Nevertheless, the positive facts 
are closely and very remarkably in accord with the genetic clas- 
sification of the species as traced out graphically in lines spreading 
from a centre in Psil. planorbe or caliphyllum , and with the subse- 
quent cycle in the life-history of the individual and of the series 
to which the individual belongs. 
Whether it will be ultimately demonstrated that all the faunas of 
the Lower Lias were derived by chorological migrations, and corre- 
sponding modifications, from radical forms which arose in the three 
autochthonous basins mentioned above cannot now be discussed. 
So far, however, as American forms are known to us, they have a- 
distinctly European facies . 1 The geology of North America also 
supports the conclusion that the Jura was neither very completely 
1 Caloceras Ortoni from Chacapoyas in north Peru can only with difficulty be sepa- 
rated from the stouter varieties of Caloceras salinarium described and figured by 
Wahner from the Northeastern Alps, and a form of Cal. nodotianum lately received from 
Peru cannot be separated from some varieties of that species in Central Europe. The 
South American province includes the Jura of the Argentine Republic, Chili, and 
Peru. This fauna besides a number of peculiar species is composed of a mixture of 
Central European and Mediterranean species. The North American province includes 
California and Vancouver’s Island. These faunas over and above their own peculiar 
species are mixtures of European forms. 
