ß/j2 Frits Johansen. 



algae (see below). At places where the currents are strong (sounds, 

 mouths of fjords) the littoral region is almost entirely wanting or 

 rather, it is one with the Laminaria region, as we often find the 

 brown algae mentioned already at ca. 2 m along with the littoral, 

 green algae. At the same time, if the depth permits it, the Lami- 

 naria vegetation may go out to greater depths than elsewhere (down 

 to ca. 20 m), probably because the salinity of the water and the 

 current here afford it excellent conditions of growth. But however 

 great the extension of the Laminaria region may be, it attains its 

 greatest profusion and most typical appearance between 5 — 10 m. 



At a depth of ca. 15 m the algal vegetation consits of the 

 foliaceous Rhodophyceae, Delesseria sinuosa, Polysiphonia arctica, 

 Phyllophora etc. and the Corallinaceae, Lithotamnion laeve, Cruoria 

 arctica etc. The last are most predominant, clothing the many, 

 loose stones, shells of animals etc., whilst the Florideæ are more 

 scattered. I call this form of vegetation therefore the Lithotam- 

 nion region and use the name Delesseria region for the corre- 

 sponding algal vegetation on the soft bottom. I take 20 — 40 m for 

 the characteristic depth of the Lithotamnion region, that is, this 

 vegetation reaches its maximum here, even though found in shal- 

 lower and deeper water. At a few places indeed it is found at a 

 surprisingly shallow depth (ca. 10 m), as the Laminaria region for 

 one reason or another only reaches out to this; and in general its 

 transition to the following deeper region, the Hydroid region, is 

 quite even (first the foliaceous and later the calcareous algae be- 

 coming fewer and fewer). This characteristic vegetation, which 

 attains its richest development at ca. 50 m, consists of more or less 

 dense mattings of hydroids (of these not a few Lafoea fructicosa, 

 Sertularella Iricuspidata are already found in the Lithotamnion region), 

 including Lafoea serpens and Halecium muricatum, in addition to a 

 few which are common to these two regions, e. g. Cuspidella pro- 

 cumbens, Eudendrium rameum^. 



These hydroids find excellent conditions for their growth on 

 the many, loose stones, mollusc shells, Balani etc. along with the 

 algae; and to how great an extent they are bound to these is seen 

 from the fact, that here and there we find spots with sand and 

 gravel (probably with rock underneath), where the vegetation is 

 extremely sparse, as also from the fact, that this region is quite 

 wanting on the soft bottom which is free of stones. Passing still 

 further out (to over ca. 50 m) the hard bottom appears as banks 

 here and there; the algal vegetation is still thinner and the hydroids 

 change their character at ca. 100 m (other species: Lafoea grandis, 



^ See also "Report on the Hydroids" by P. Kramp in this work, Bd. V, Nr. 7. 1911. 



