676 
Proceedings of the Roycd Society 
The animals captured at the stations surrounding North Bona all 
belong to known British species. 
What is the legitimate limit of the “British fauna”'? Are the 
Faroe Channel animals to be included in it 1 These are questions 
which have been often asked, and, although they appear to us 
unimportant, yet are not without interest. 
When we regarded the marine fauna as having a depth limit, the 
question answered itself — the British fauna ended doubtless with the 
existence of the fauna. Now, since we know that the marine fauna 
has no depth limit, we must, if we wish a limit, fix an artificial 
one. 
Temperature is the most important factor in the distribution of 
marine species. The mean annual temperature of the ocean and of 
the shallow water around coast-lines varies from about 29° Fahr. in 
the polar regions to about 75° Fahr. under the equator. This great 
inequality of temperature is the limiting cause of the distribution of 
marine species, both at the surface of the sea and in shallow water. 
Pelagic species have a marked and limited distribution depending 
on temperature, — quite as much as species inhabiting the shore 
waters, — and this distribution can be traced on the bottom of the 
ocean in many instances. 
By an examination of an oceanic deposit, it is possible to tell 
approximately its latitude from the character of the dead shells of 
surface organisms found in it. The depth from which the deposit 
came, and also its longitude, can in many instances be approximately 
determined by careful microscopic examination of the fragments, 
organic and inorganic, of which it is composed. WTiile the surface 
of the ocean, like the surface of the land, has its climates, it is quite 
otherwise with the deep sea. 
The mean temperature of the bottom of the ocean is about 35° 
Fahr., so that an enormous expanse of the sea-bottom, covering nearly 
three-fourths of the surface of the earth, is under circumstances 
where there is no bar to general diffusion, and the result is that this 
vast area, with a temperature say under 40° Fahr., admitting of free 
migration, is inhabited by a fauna whose most marked characteristic 
is extreme uniformity. 
The temperature of 35° Fahr. rises in the polar regions towards 
the surface, and we should expect therefore that the shore and deep- 
