NORMAN: ON THE MOLLUSCA OF BERGEN FIORDS. 6^ 



gallina, Psa7nviobia tellinella, Cyrtodaria siliqua, CocJilodesma 

 p-(ztenue, Littorina littorea, Rissoa cingellus, Lajjiellidorls incon- 

 spicua. 



In the following notes on the Geographical Distribution of 

 the mollusca which have just been tabulated, I shall indicate what 

 I consider to be the home of species by the following letters: — 



O. — Oceanic. E. — European. 



A. — Abyssal. P. — Polar. 



E. A. — Eastern American. 



O. — Oceanic. Species which swim or float freely on the sur- 

 face, and are not confined to any shore, their distribution 

 being chiefly governed by the temperature of the su/face water. 



A. — Abyssal. Species which live at great depths, scarcely 

 ascending to the hue of loo fathoriis' soundings. They are 

 subjected to great pressure^ and inhabit so great a depth of 

 water that the temperature is but slightly, if at all, aff"ected 

 by the seasons of the year and heat or cold of the surface. 

 These forms have a very extended distribution, being inde- 

 pendent of those climatic conditions which afl'ect animals 

 living at lesser depths. 



E. — European. These are littoral forms, which, though they 

 may descend below the loo fathoms' soundings, are for the 

 most part much more abundant in shallower water. They 

 may have originated on any part of the European coast, and 

 have ranged thence north or south; but their distribution, 

 even though it has extended to America, has been along the 

 coast-line. They cannot live in the abyss any more than can 

 the abyssal animals endure the lesser pressure and changeful 

 temperature of shallow seas. 



P. — Polar. These animals form a most important feature in 



