[MATTHEW ] CAMBRIAN FAUNAS 105 
An increase in the elevation of the ventral valve (see fourth 
column) is quite as noticeable in this genus as in Acrotreta as it is 
found in the Basal Cambrian; but so far as bulk of the valve is con- 
cerned the two genera differ, for Acrothyra shows no increase, but 
on the contrary, if anything, a reduction in bulk. It would seem to 
have been a closed type, which had reached its culmination and was 
not capable of further development. 
No. 7. Dip THE UPPER ETCHEMINIAN FAUNA INVADE EASTERN 
CANADA FROM THE SOUTHEAST? 
Some years ago, when president of Section IV. of this Society, 
the writer had the honour of asking the attention of the members of 
this section to certain conditions of the fauna and sediments of the 
early Paleozoic in the North Atlantic region, that seemed to indicate 
the manner of the migration of animal species at certain times from 
one side of the Atlantic to the other; the faunas in some cases being 
borne from Europe to America, and in others from the latter continent 
to Europe. 
These conjectures in regard to the migration of species were based 
largely on the known spread of the genera from certain provinces 
where the faunas were in full force, to others where they were repre- 
sented by a limited number of species. 
For instance, the Paradoxides fauna, of which Anopolinus is a 
member, appeared to have its headquarters in Northern Europe, for 
there not only does it have the greatest variety of genera, but it also 
shows the most continuous chronological suceession. Anopolinus, 
while it is found in Scandinavia and Britain and extends as far west 
as Newfoundland, has not been found in Canada. And the species 
of Paradoxides abundant in Europe and well represented as far as 
Maritime Canada, is reduced to one species (or two) in Massachusetts, 
and west of this is unknown. 
A representative form of one species of this fauna, a Liostracus 
(the Conocephalites tener of Hartt), which we had thought to be pecu- 
liarly American, was sent to me this summer from the south of France, 
by Mons. Jean Miquel, it thus also proves to be European, but belongs 
in the southern facies of this fauna, represented in Paradoxides 
rugulosus and the associate species. The American fauna of Para- 
doxides thus drew its representatives from both the northern and 
southern provinces in Europe. It would be an instructive study to 
ascertain how and why the northern fauna of Paradoxides prevailed over 
the southern in Maritime Canada, and what held the Upper Fauna of 
