154 H. JONSSON 



community or quite similar communities: the sublittoral Floridecv- 

 formation. 



17. The Lithothamnion-association. 



In this association I include only the highly branched species, 

 Lithothamnion Ungeri and L. tophiforme, as these differ from the 

 other calcareous algal vegetations by their characteristic and very 

 social growth. Within the fjords, at a depth of about 12 — 25 metres, 

 these algae occur in such abundance that there might be good 

 reasons for calling it a submarine reef of calcareous algae. Within 

 Arnarfjorimr in the vicinity of Bildudalur there was, for instance, 

 such a luxuriant vegetation of L. Ungeri that the dredging-bag was 

 filled time after time, nothing being found in it save this species. 

 Mr. B. Saemundsson has also found a similar Lithothamnion 

 vegetation in several of the small fjords at Isafjar5ardjup; and as, 

 moreover, there are specimens to hand from several other fjords 

 in NW. Iceland, this association seems to be luxuriantly and com- 

 monly distributed in this part of the country. A similar vegetation, 

 mainly composed of L. tophiforme, occurred also in abundance in 

 EyjafjorOur in N. Iceland. I have also noticed a similar vegetation 

 — though not so luxuriant — in several of the fjords of E. Iceland. 

 Horring collected L. tophiforme in Hvalfjor5ur in SW. Iceland, and 

 Saemundsson also found it there, apparently growing very socially. 



In this association very few epiphytes occur, though Turnerella 

 Pennyi ought to be mentioned in N. and E. Iceland ; on the other 

 hand animals generally occur in abundance, especially Ophiurida 

 and snails and other smaller molluscs which project everywhere 

 from between the Lithothamnion-hranches. 



When dredging on such a bottom rather large pieces are hauled 

 up, which cohere, usually, by reason of the numerous branches 

 being matted together. Rather large globular masses, which are 

 sometimes hollow, but which are often filled with comparatively 

 thick interwoven branches, are also frequently obtained. The hollow 

 masses must be supposed to have grown on the outer side of some 

 substratum which has disappeared. This ^Egagropila-form is gene- 

 rally known. Rosenvinge mentions it from Greenland, and assumes 

 that it lies loose upon the bottom ; the masses must then be illu- 

 minated all round by being rolled about as, for instance, by the 

 action of the undercurrent. From what I have seen, it seems to 

 me that a point of attachment can be perceived on entirely fresh 



