OF PLYMOUTH AND THE ENGLISH CHANNEL, 



257 



NOTE ON PRUVOT'S BIOLOGICAL REGIONS. 



Pruvot (29) bas dealt at some length with the fauna of the coast of 

 Brittany and that of the Golfe du Lion in the Mediterranean. 



In comparing the faunas of these two regions he shows how the life of 

 the various species is intimately related to the conditions to which they are 

 exposed, and the character of the surface on which they live. 



I have here incorporated a summary of his observations in so far as they 

 apply to the group under consideration and as regards the Channel fauna 

 only. 



It will be seen that his observations very accurately describe the dis- 

 tribution of PolycliEetes in the neighbourhood of Plymouth, but reference 

 must be made to his work for one to realise its importance. 



As his terminology differs from that in general use in this country it needs 

 some explanation. He divides the depths of the sea into three regions : 

 (1) Littoral, (2) Coastal, and (3) Abyssal, the last of which is not, of course, 

 found in the Channel. 



The littoral region is that in which the bottom is subjected to the influence 

 of waves and superficial currents, and extends so far as to include the 

 laminarian and a considerable portion of Forbes' coralline zone. The coastal 

 region occupies the whole of the Channel below a depth of about 21 fathoms. 



The following table will show better than mere description the subdivision 

 and character of these regions and the three " facies " ascribed to each zone : — 



