INVERTEBRATE BOTTOM FAUNA 547 



the two faunas led to a closer examination of certain forms 

 which had formerly been looked upon as common to both areas, 

 and as a result the Danish zoologist Jensen came to the con- 

 clusion that not a single species of Lycodes belonging to the 

 cold area occurs in either the Atlantic or the boreal parts of the 

 Norwegian Sea. He further succeeded in showing that one of 

 the most characteristic mussels of the cold area, formerly 

 designated Pecten fragilis and included as such among the 

 fauna of the Northern Atlantic, is in reality a form peculiar to 

 the cold area of the Norwegian Sea, and he has accordingly 

 named it Pecten frigidus. Other naturalists have made similar 

 discoveries in the case of a number of other forms. Thus, the 

 irregular sea-urchin of the Norwegian Sea, P ourt ale sia Jeffrey si, 

 is quite distinct from the Atlantic forms of the same genus. 

 The characteristic starfish of the Norwegian Sea, Bathybiaster 

 vexillifer, was formerly said to be distributed throughout 

 the Atlantic, but it is now known to be different from the 

 Atlantic form, which is Bathybiaster robiistzis. Another starfish, 

 Pontaster temcispinus, is represented by different varieties in 

 the two areas, and the same is true of the ophiurid Ophioden 

 sericetuji. The one characteristic pennatulid of the Norwegian 

 Sea, Unibellula encrintis, is not found outside that sea, though 

 there is a species closely related to it in the Atlantic, namely, 

 Umbelhtla li?tdak/i. Further evidence of the difference in the 

 two areas is supplied by a pycnogonid belonging to the genus 

 Colossendeis. A form in the Norwegian Sea deep basin, 

 Colosseiideis ano^usta, is said to occur also in the Northern 

 Atlantic, but if we compare Atlantic and Norwegian Sea speci- 

 mens we immediately recognise considerable differences in 

 their structure, the latter being much more robust and furnished 

 with shorter legs and claws. Any one seeing the two forms 

 side by side would be able to tell the respective areas from 

 which they came, though it may be difficult to find sufficient 

 dissimilarities to designate them separate species. 



^hese are merely a few instances. It must be admitted Coidarea 

 that nothing like a complete comparison of the species has yet Norwegian 

 been made, but we know enough to justify us in looking upon Seaanarctic- 

 the cold area of the Norwegian Sea as a distinct deep-sea faunal ^ ^^^^ ^'^^^' 

 region, which with Mortensen and Jungersen we may term the 

 arctic abyssal.^ No doubt, this arctic-abyssal region owes its 



1 In my description of the fauna in the cold area on pp. 517-524, I have made a distinction 

 between the continental slopes and the abyssal region below 2000 metres, but no such distinction 

 has been made here, for in instituting a comparison between the fauna of the cold area and the 

 fauna of the Atlantic, I have included everything below 800 metres. 



