HYDROIDA II 



107 



Sertularella rugosa must be characterised as a boreal species, having its bathymetrical distri- 

 bution in the upper half of the littoral region, though it does not often penetrate up into the tidal 

 zone. Kirch enpauer (1884) records it as found at Greenland, but there are no subsequent finds 

 recorded from there. In the areas investigated (fig. LVIII) it has, it will be seen, an easterly distri- 

 bution from Iceland to up in the Barents Sea, but its occurrence in the purely arctic area is quite 

 sporadic, while on the west coast of Norway, for instance, it is a characteristic species in the laminaria 

 zone. New finds are those from the Faroe Islands, where the species might be expected to be found 

 from its occurrence off the coasts of Iceland, the British Isles, and Norway. 



200 m. . 600 m. ._ 1000m. 



Fig. LVIII. Distribution of Sertularella rugosa in the Northern Atlantic. 

 In the hatched regions a common occurrence is noted. 



Diphasia Agassiz. 



Upright colonies, the hydrotheca; having a horizontal or, slightly obliquely situated aperture 

 without distinct teeth, but as a rule witli an adcauline sinus, in which the large single opercular plate is 

 attached. The polyps have, as far as can be seen from external observation, no abcauline blind sack. 



This definition differs in one important feature from that given by Lev ins en (1913 p. 309), 

 the organisation of the polyps being taken into consideration. We thus obtain a stronger and more 

 natural limitation, and the genus then practically coincides with the group Eudiphasia Broch. It has 

 long been a doubtful question whether the two groups Eudiphasia and Abietinaria should be assigned 

 generic rank or not, attention having previously been paid only to the form of the hydrotheca as the 

 decisive point, and distinction thus made between species having more cylindrical hydrotheca; or hy- 



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