No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 5 



As I have earlier pointed out, these algae require, in order to 

 thrive, a firm, or fairly firm, bottom, but principally a fairly strong 

 movement of the water, i. e. places where the tidal waters run 

 rather strongly. Besides the bottom must be fairly even, to render 

 the formation of banks possible. On the other hand, it may be 

 of partly destructive effect if the tidals run too strongly, or if the 

 plant appears in places with very strong currents. Particulars 

 about this state of things will be found below. 



In places where the Lithothamnia thrive and occur in some 

 number, there is — as a general rule — also a rich fauna. Most 

 calcareous alga? — as I have earlier often mentioned — are to 

 a great extent attacked by lower animals, particularly small ones, 

 or serve as the residence of a lot of such ones — in the first 

 instance of worms, then of echinoderms, peculiarly smaller forms, 

 e. g. ophiurida, of mollusks 1 ), peculiarly boring-muscles (saxicava), 

 partly also of echinida and Crustacea. This is either wholly or 

 partly destructive, or at any rate checks the normal development 

 of the plant, and may often cause the rise of greatly varying forms 

 of one and the same species. This concerns both crustlike and 

 branching species 2 ). By a repeated overgrown of new hypothallium 

 so as to cover the extraneous objects, and on the whole by a more 

 vivid vegetative activity, the alga endeavours to defend itself against 

 this destructive influence. Thus even the cells — particularly 

 the hrypothallic cells — will often grow considerably longer than 

 in normal conditions. The occurrence of overgrowing hypothallium, 

 as a matter of course, can also be owing to the fact that 

 germinating plants attach themselves to and are developed on older 

 specimens of the same species. However, even a sparsely branching 

 species freely developed at the bottom will occasionally develop 

 crustlike formations, when the alga comes in contact with foreign 

 bodies, or certain lower animals attach themselves to it 3 ). 



!) M. Foslie. (M. F.). Alger og Muslinger. — Naturen. Bergen 1892. Pag. 17. 

 2 ) M. Foslie. The Lithothamnia of the Maldives and Laccadives. — The 



Fauna and Geography of the Maldive and Laccadive Archipelagoes — Vol. I. 



Part 4. Cambridge 1902. Pag. 460. 

 3 J A. Weber-van Bosse and M. Foslie. The Corallinaceae of the 



Siboga-Expedition. — Siboga-Expeditie LXI. Leyden 1904. Pag. 22. 28. 36, 41. 



