INVERTEBRATE BOTTOM FAUNA 507 



etc. It must, however, be clearly borne in mind that there were 

 many forms common to both areas, — partly those which belong 

 to the entire boreal region, and partly those which are ex- 

 clusively or nearly always found on the plateaus. 



As already stated, the bottom on the plateaus rarely, and Fauna of the 

 as a rule only in deep hollows, consists of soft mud, being for 

 the most part coarse or fine sand, sandy mud, stones, and rocks. 

 The stony bottom usually predominates near the outer limits of 

 the plateaus, or continental edge. Investigations by Rasch in 

 1844 and by Sars in 1871 made it clear that large round stones 

 and pebbles are to be met with on the Great Edge to the west 

 of Aalesund at a depth of about 200 metres, and the " Michael 

 Sars " also found round stones and pebbles there, as well as on 



continental 

 edge. 



Fig. 354. 

 Dorocidaris papillata, Leske. Reduced. (After Diiben and Koren. ) 



the rather less sharply defined edge of the Faroe plateau ; in 

 the latter locality the dredge brought up from a depth of about 

 400 metres a mass of loose round stones. 



The character of the fauna on the edges of the boreal 

 plateaus, judging from what we have found on the Faroe and 

 the Norwegian plateaus, is fairly uniform. Owing to the nature 

 of the bottom we meet with attached forms, particularly sponges 

 (for instance Oceanapia robusta), hydroids, corals, brachiopods, 

 and bryozoans, together with a number of unattached forms, 

 of which the echinoderms are the most characteristic. Among 

 brachiopods we get Crania anotnala, Terebratulina caput- 

 serpentis, Waldheimia cranitwi, and W. septaia, the last of 

 which inhabits the plateaus of the open sea and never or 

 only exceptionally enters the fjords. The same is the case 

 with several echinoderms: Dorocidaris papillata (see Fig. 354), 



