24 



STYLASTERIDAE 



must be regarded as characteristic forms of the large biocoenosis of the coral reefs. This is also 

 strengthened by the single discover)- of Stylaster gcmmasccns made in the Hjelte Fjord in the 

 neighbourhood of Bergen, where Dr. O. Nordgaard has obtained two small fragments of colonies 

 from the coral reef there. 



We thus see that the two Stylaster species which occur on the coast of Norway, form interesting 

 parallels in the animal community of the northern coral reefs to the Stylasterids of the tropical coral 

 reefs. They are thu.s, like the Lopliohclia reefs as a whole, bound in their occurrence to those localities 

 witii hard bottom, where the Atlantic current makes its influence most felt in the Norwegian Sea. 



0° 



A Pliohothnts symmetrii'us 



A — — iiicompl. geograph. data. 



9 Stylaster gemmascens 



O — roscus 



+ — (Allopora) norvcgicus 



Text-fig. I". Maj) showing the locaUtics of the Stylastcridac in the North Atlantic aud the Norwegian Sea. 



200 111. depth 

 -- 6oo - ^ 

 , _ 1300 - — 



The study of the occurrence of the North Atlantic Stylasterids shows several biogeographical 

 features of interest (cf. Chart Text-fig. F). — Pliobothrus synwietricns was first described from the waters 

 round about F'lorida and must be fairly common there between 190 and 300 metres. It has been found 

 by the »Ingolf« on the steep slope off the south coast of Iceland towards the depths of the Atlantic 

 in 594 and 658 metres. According to Duncan (1874 p. 336) the .>Porcupine« obtained a single specimen 

 in the cold area of the Faeroe Channel; unfortunately he does not state the exact locality. We thus 

 have a species here which belongs to the warm Atlantic waters and normally is not able to penetrate 

 in over the submarine ridge, which towards the south separates the Norwegian Sea from the depths 

 of the Atlantic. The one find in the cold area must be a pure chance and forms a parallel to the 

 single aud scattered finds which have been made here aud there in the Norwegian Sea of other 

 typical warm water forms among the Hydroids. 



