The Botany of Iceland - 01.12.1912, Qupperneq 168

154
H. JÓNSSON
community or quite similar communities: the sublittoral Florideœ-
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 algæ occur in such abundance that there might be good
reasons for calling it a submarine reef of calcareous algæ. Within
Arnarfjörilur 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 tliis species.
Mr. B. Sæmundsson has also found a similar Lithothamnion
vegetation in several of the small fjords at Isafjarðardjúp; and as,
moreover, there are specimens to hand from several otlier 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
Eyjafjörður in N. Iceland. I have also noticed a similar vegetation
— though not so luxuriant — in several of the fjords of E. Iceland.
Hörring collected L. tophiforme in Hvalfjörður in SW. Iceland, and
Sæmundsson also found it there, apparenlly growing very socially.
In this association very few epiphjdes occur, though Turnerella
Penngi 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 wliich project everywhere
from between the Lithothamnion-branches.
When dredging on such a bottom rather large pieces are hauled
up, which cohere, usually, by reason of the numerous branches
being matted together. Bather large globular masses, which are
sometimes liollow, but wliich 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 Ægagropila-íorm is gene-
rally known. Rosenvinge mentions itfrom 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