186 Barrande— Origin of Paleozoic Species. 
beginning of’ the second fauna, the beginning of the third 
fauna, and the end of the third fauna. We observe, also, that 
of the third fauna we can count only 4 or 5. We do not know 
ny reason to be assigned for these fluctuations. They are 
particularly well marked in the basin of Bohemia, doubtless on 
account of its great richness. * * About the beginning of 
the third fauna, the 12 existing types show a development of 
specific forms which constitute the absolute maximum 0 
the Silurian, viz, about 1000 species. This is principally due 
to the contribution furnished by Bohemia, viz: 746 species. 
IV. Parallel between the chronological and zodlogical evolution of 
Cephalopods.—Concordance between geological and zodlogical 
evolution should be plainly shown, if the more simple forms of 
zodlogical evolution had appeared first, and if, on the other 
hand, the more vaicgitiodaad forms had appeared Jast, in the 
series of Silurian epochs. Now, observations of facts shows us that 
precisely the contrary has occurred. In fact, according to exist- 
ing documents, the more simple forms, viz: the Ascoceratide, 
appeared only toward the end of the second fauna in Canada, 
other hand, the more comple rms, suc Nautilus and 
Trechoceras, are manifested from the beginning of the secon 
fauna, in Ameri These facts suffice to show us the 
and the chronological evolution of Silurian Cephalo 
But we have also noted, in the course of our studies, other 
facts, which confirm this discordance, and which are inexplicable _ 
by the transformation theory. The principal ones are as follows : 
regions, about the beginnin i 
accord with the idea of their slow and successive derivation 
hemia, within a very narrow horizontal area, and the 
