56 
lands off the west coast of South Jutland and at Læsø. Very marked 
animal communities, differing conspicuously according to the charac¬ 
ter of the bottom, sandy or muddy, have their home in such localities. 
Only the sandy flåts have been described in the present paper. Two 
distinet communities are found on the sandy flåts, the Corophium- 
Pygospio community occupying the inner, more shallow part, the 
Ar enicola-Cardium community the outer, less shallow part. As 
regards Corophium and Arenicola reference should be made to the 
paper by Warming and Wesenberg-Lund quoted above (p. 24). 
Cardium edule, which lives here in very great numbers (ca. 800 til 
1000 pr. □ M.), was observed often to move for some distance, 
— a few decimeters — by means of its foot, thus being not so 
very sedentary. Its exerements were seen to form quite conspicuous 
masses, when washed together by the wavelets, this species having 
thus some importance as a mud forming factor. Pygospio elegans 
Clap. is the most numerous of all, its sandy tubes sitting so close 
in the bottom as the blades of grass in a grass field — ca. 35— 
40,000 pr. □ M. It is thus, like Corophium an important mud- 
binding factor. The faet that it protects its brood (cf. Soder- 
strom; op. cit.), the larvæ having no pelagic stage, accounts for 
the extraordinarily great numbers in which this species occurs. — 
A very rich microscopical life is found in the thin layer of brown 
mud on the surface of these flåts: Copepods, Ostracods, Nema- 
tods, Infusoria, Diatoms etc. 
The large sandy flåts at the Southend of Læsø have a some- 
what different character. The surface layer is here woven together 
by innumerable Cyanophyceæ. The animal forms dominating here 
are Hydrobia ulvæ and Pygospio elegans; also Nereis diversicolor is 
very numerous in some places. The microscopical life of the bottom 
is wonderfully rich, consisting mainly of the same forms as those 
of the Fanø-flats. — In a somewhat similar locality at Køge (See- 
land), the dominating forms were Hydrobia, young specimens of 
Cardium edule, and Paranais littoralis. The Cyanophyceæ were 
only slighthy developed here. 
1 — 10—1921. 
