vi ECHINODERMS OF THE BRITISH ISLES 



and the Cape Verde Islands, have been found to occur also in the 

 British deep-sea area, and inversely. The author was thereby 

 led to the conclusion that the whole of the north-east Atlantic 

 deep sea, from the Azores and the Cape Verde Islands (perhaps 

 even Ascension) in the south to Iceland in the north, forms one 

 single zoogeographical area, and that all the species known 

 from any place within that area may be expected to be 

 distributed all over it, and thus to occur also off the British 

 coasts in suitable depths. Therefore, again, to confine the work 

 only to those species actually known from the British area 

 would mean that in all probability the work would very soon 

 prove to be incomplete, as it is to be expected that any deep- 

 sea dredgings off the west coasts will bring to light species not 

 hitherto found within the British area. The same holds good 

 of the cold area of the Faroe Channel, as it may well be expected 

 that the whole of the fauna characteristic of the deep-sea area 

 of the cold Norwegian sea will prove to extend as far south as 

 the cold, deep water proceeds, thus to within the British area. 



The author therefore has thought it desirable to comprise all 

 those deep-sea forms which may reasonably be expected to occur 

 within the British area, though not yet actually known from 

 there — just as in the Danish work all the species which may 

 reasonably be expected to occur, e.g. in Skagerrack, though 

 not yet known from there, have been included. While full 

 descriptions and figures are given of all the species knoAvn to 

 occur within the British area, the species expected to occur 

 there — though not yet actually found — are less extensively dealt 

 with ; only their main characters, necessary for the identi- 

 fication, are given in the keys, usually with reference to the 

 chief works where full descriptions and figures of them are to 

 be found. In this way it is hoped that the book will remain 

 useful also in the future, when many more species shall have 

 been added to the British fauna. 



A very striking case, showing the correctness of the course 

 thus adopted, happened, before the manuscript was com- 

 pleted. A small collection of echinoderms from off the Irish 

 coasts, which was sent me by Mr. Farran, proved to contain 

 no less than three genera and species new to the British fauna, 



