. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. i84 HYDROIDA II One risk attaching to the insertion of the mentioned boreo-arctic and Lusitanian mixed areas lies on the one hand in the fact that by such further division, the whole arrangement is rendered less easy to survey and handle. If, however, other and more essential advantages were procured by so doing, we should naturally not hesitate to accept the biogeographical sub-areas in question But here a very serious difficulty makes itself felt, more particularly on considering the gro
. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. i84 HYDROIDA II One risk attaching to the insertion of the mentioned boreo-arctic and Lusitanian mixed areas lies on the one hand in the fact that by such further division, the whole arrangement is rendered less easy to survey and handle. If, however, other and more essential advantages were procured by so doing, we should naturally not hesitate to accept the biogeographical sub-areas in question But here a very serious difficulty makes itself felt, more particularly on considering the group of hydroids as a whole, to wit, the question of how far up in the boreal area — sensu laterior — the intermix- ture of southern elements takes place to such a degree that the waters concerned should be regarded as a mixed area. By way of illustration we may take the distribution of the families Plniujilariidir. joo m boom. (ooo m. looom. Fig. XCIII. Finds of Plutnulariidae in the Northern .Atlantic. and Aglaopheniida^ the members of which without exception have their chief occurrence in warmer and more southerly waters, and must in the boreal region be regarded as southern visitors, even though some few of them, such as Nemertesia antennina, and Kirchmpaueria pmnata, may here and there occur in considerable numbers. We should note then, that Phimuhniidcr (fig. XCIII) which save for one or two exceptions belong to the upper 300 metres, are found ~ and found ver>- frequently - in the North Sea and along the west coast of Norway, including the Trondhjem Fjord, round the Faroe Islands, along the east, south and west coasts of Iceland; indeed, several species ha\'e even been met with several times on the borco-arctic Lille Hellefiskebanke in Davis Strait. Judging from the family PlumulariidcB then, we come to the result that the Lusitanian element plays a very prominent part m the heart of those areas which we have hitherto designated as the boreal; so much so indeed, that
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Keywords: ., bookcentury1800, bookdecade1890, booksu, booksubjectarcticregions
