504 DEPTHS OF THE OCEAN chap. 



approximately 300 or 400 metres, till we come to the inner 

 portion of the Skagerrack where it increases to about 700 

 metres. The bottom consists of soft mud throughout, except 

 for a long narrow strip of stones and rock that penetrates its 

 north-eastern portion. On the one side the depression is 

 bounded by the Norwegian coast-plateau, which is here only a 

 few miles wide, and on the other side by the plateaus of the 

 North Sea and Skagerrack. 



During the cruise of the " Michael Sars " in 1902 investiga- 

 tions were made with the trawl and dredge in its northern 

 portion, the principal forms found being as follows : — 



Echinoderms : SticJiopus tremiihis (in quantities), Bathyplotes tizardi^ 

 Cucinnaria hispida, MyriotrocJms vitreus, A mphiura norvegica, Ophioscolex 

 glacialis, OpJiiura sarsi, Aster onyx loveni (on Funiculind), ScJiizaster 

 fragilis, Bj'issopsis lyrifera, Spatangus rascJii, Psilaster andromeda, 

 Pontaster tenuispiniis. 



Crustaceans : PontopJiilus norvegicus, Pandalus bonnieri. 



Ascidians : Ascidia obliqua. 



Molluscs : Abra longuallis, Malletia obtusa, Portlandia lucida, 

 Axiniis flexuosus, Pecten septeinradiatus, Sipho islandicus, Scaphatider 

 punctostriatus, Antalis agzlis, SipJionentalis tetragona, Caduliis 

 subftcsiforni is. ^ 



Worms : Lumbrinereis fragilis, LcEtinonice filicornis, Aricia sp., 

 Terebellides str'dmi. 



Gephyreans : Sipunadus priapuloides. 



Ccelenterates : Bolocera ttiedzce, Actinostola callosa, KopJwbelemnon 

 stelliferuiii^ Fiinicidina quadrangularis , UlocyatJius arcticiis. 



Sponges : Thenea muricata. 



Also the foraminifera AstrorJiiza and RJiabdamniina, though these 

 are not numerous. 



These animal forms make it tolerably certain that the fauna 

 in the Norwegian depression is practically identical with the 

 Atlantic fauna in the boreal region of the Scandinavian 

 peninsula, and closely resembles the fauna of the western 

 fjords of Norway. Petersen's researches have revealed 

 similar conditions in the deepest portion of the Skagerrack. 

 But along with the fjord forms, which exceed the others in 

 numbers, there is a fauna in the Norwegian depression composed 

 of forms seldom or never occurring among the skerries and in the 

 fjords, but having their home on the plateaus of the open sea.'^ 



^ On the other hand, Mesothuria intestinalisYiz.'i not been found by the "Michael Sars" 

 nor by other Norwegian and Danish Expeditions. 



^ This species was found by the Norwegian North Atlantic Expedition. 



3 To this fauna I assign the following forms : — Echinoderms : Spatangus raschi, Pontaster 

 tenuispimis •■, Molluscs: Sipho islandicus, Antalis agilis ; Crustaceans: Pandalus bonnieri; 

 Coelenterates : Ulocyathus {Flabelliim) arcticus. 



