INTRODUCTION. CXV11 



these rather less than half are common to the two 

 countries. 



About 100 British species occur on the more south- 

 erly coasts of Norway, and about 70 within the Arctic 

 region ; no distinctively southern forms, I believe, are 

 met with amongst them. About 50 of our species range 

 to the North-American coast, almost all of which have 

 been recorded from the Arctic seas *. 



It is interesting to compare the number of species 

 found in three well-marked districts (each of which has 

 been thoroughly investigated) the south-west coast of 

 England, Shetland, and portions of the north-east coast 

 of England f- 



Northumberland 



137 139 89 



Turning to the distribution of our British species in 

 time, we find that a considerable number of them existed 

 iu the Tertiary period. Many are recorded by Busk ; 

 and about 4O are included in the list of the Upper Tertiary 



* We may expect a flood of light to be thrown on the subject of distribu- 

 tion by tlii' result* of the 'Challenger' expedition, when published. In 

 their absence it would hardly be safe to indulge in generalization. 



t Alder, ' Catalogue of Zoophytes of Northumberland and Durham ' and 

 Supplement. Norman, "Shetland Polyzoa," Rep. Brit. Assoc. 1867. Ilnirky, 

 "Catalogue of Zoophytes of South Devon and Cornwall." The Shot land 

 and South-west lists have been revised; the North-east is as given by Alder. 



