HYDRO IDA II 



185 



family Aglaoplicuiida: (fig. XCIV) we nuist first of all bear in mind that we are here dealing with 

 the hydroid family which contains most true deep-sea species, so that we get a picture esseutiallv 

 different from the previous one. Yet there are also various resemblances ob.servable. The boreal 

 bottom region is, as will be evident from the foregoing, a restricted part of the typical coast bank 

 region which runs down to about 600 metres depth. Up in this region, Aghioplicniida; penetrate more 

 rarely, but are yet not infrequently met with in the North Sea and along the coast of Norway, and 

 may even in certain places be character forms, as for instance in the deep parts of the Trondhjem 

 Fjord, where there is much current. The numerous finds group themselves about the Wvville-Thom- 



- 2OQ m. 6com. ___fooo/n. .. _. __ _.rooofn. 



P'ig. XCIV. Finds of Aglaophciiiidae in the Northern .Atlantic. 



son ridge, and of these, about half lie, mirabile dictu, down in that part of the cold area whicli juts 

 out into the Faroe Channel. In Danmark Strait, also, the finds are gathered about the top of tlie 

 threshold, and distribute themsehes from here round the north side of Iceland. In Da\-is Strait, 

 the finds are closest in the north-eastern part of the cul de sac running from the Atlantic Deep up 

 the western side of Greenland to the north side of Lille Hellefiskebanke. In this manner then, tlie 

 intermediate parts between the aforementioned areas, where the strong intermixture of Plumnldriicla 

 sets its mark on the fauna, are levelled out. And to be entirely consistent, we should perhaps also, 

 in the Faroe Channel, include a lusitano-arctic mixed area. 



The data here given serve to show that the establishment of the mentioned mixed areas, the 

 boreo-arctic and the boreo-lusitanian, is attended by considerable drawback.s. No boundary of any 

 region, of course will ever be perfectly clear and sharp, especially in the case of bottom form.s. There 

 are too many factors to be considered, with the result tliat the frontier as a matter of fact comes to 



The Ingolf-Expedilion. V. -. '^*+ 



