292 
HULLETIX OF THE NATURAL HISTORY SOCIETY. 
a greatly diluted form, may make possible the presence of 
species which, were it not for the presence of some degree of 
salinity, would probably not he found at all in such waters. 
It has been found also that the commingling of fresh and salt 
waters affects the character as well as the number of species 
occurring where such admixture takes place, the usual effect, 
whether the transfer of habitat he from fresh to salt water (u* 
the reverse, being the diminution in the amount of silica secreted, 
and the consequent decrease in the clearness of striation and 
sometimes the complete disappearance of the latter. It is also 
altogether probable that, as with other forms of plant life, the 
Diatoms are sensitive to their surroundings, and that, among 
fresh water forms, some prefer still, others running water, some 
boggy pools or mountain lakes, hut differences of this kind have 
not yet been sufficiently studied to make any definite conclusions 
possible. 
The fresh water Diatoms possess as a group some general 
characteristics. They usually abound in attached and concat- 
enate forms, such as those of Diatoma, Meridion, Himantidium, 
Fragillaria, Tabcllaria, etc., though some species belonging to 
these genera are marine. Alost of the species of Epithcinia, of 
Eunotia and of Cymbella are confined to fresh water, while 
Naviculoid forms, like Navicula and Finnularia and Stauroneis, 
are of common occurrence, as well as attached and clustered 
forms, like Synedra, Colletoncma and Encyonema. On the 
other hand circular forms, such as Coscinodisens, and triangular 
and quadrangular forms, like Triceratium and Biddulphxa, are 
seldom or never met with. 
The abundance of Diatoms in some of the lakes of the 
Province is quite remarkable, being, in connection with other 
fresh water Algae, such as to thicken their waters to such an 
extent as to impede the passage of a boat. One illustration of 
this is to be found in what Dr. Ganong has termed Diatom lake, 
a considerable sheet of water connected with the Nepisiquit 
Diver near its head; and another is Pocowogamis Lake, near the 
main road traversing Pocowogamis Settlement in York County. 
