1G1 
The history disclosed by geological research, apart from its purely 
physical aspects, is that of the progress of life upon the globe; the 
extinction of species after species of plants and animals. and the intro- 
duction of new forms in their place. It is by means of the now 
ascertained stages of this process of change and replacement that the 
geologist is enabled to determine the age of any particular fossiliferous 
series of rocks which may come under his notice. But the scale of 
geological time is a very extended one, as compared with the progress 
of human events, and the number of animals which have been actually 
known to man and have since succumbed to process of change is very 
small. In almost every known case of the kind, man himself has 
assisted in giving the coup de grace and in completing the extermination 
of some animal which by reason of natural causes had already became 
very much restricted in its habitat. 
This, as we have seen, was the case with the sea-cow. Its hour 
had very nearly struck before the appearance of man upon the scene. 
A PLANORBIS NEW TO THE OTTAWA LIST. 
By Geo. W. Taylor, Victoria, B.C. 
While paying a short visit to Ottawa in September last, I was so 
fortunate as to discover about 40 specimens of a freshwater shell new 
to the local lists. 
The species in question is Planorbis nautilens Linn, and the 
specimens, which are all of the variety cristatus, were found in the ponds 
on the right of the road as you pass the St. Louis Dam on the way to 
the Experimental Farm. The oniy other American specimens I have 
seen of this species (which by the way is common enough in the old 
country) are two that were found by the indefatigable Mr. Hanham in 
the neighbourhood of Hamilton. 
It would be interesting to know how this species has been intro- 
duced at Ottawa, as introduced it must have been quite recently, for it 
could not have long existed undiscovered in a locality so well searched 
as the St. Louis' Ponds have been by the Ottawa Conchologists. 
