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1(54
sven o. björkman
salinity in Ihe coves of the Yoldia Sea il oughl lo endure the salinity in
the sea of today. This comparison hetween Ihe salinity conditions al
Ihe West Coast Ihen and now cannot be ful I v satisfaclorv, Ihis due to
the ahsence of lime at the present West Coast, whereas much linie is
present in the ground al the presumed relict localities. Then nothing
will be said for certain and Ihe problem must be seen also againsl the
background of the distribution of Ihe species in other parts of the world.
As is usual for species with a distribution in brackish and fresh
water, Ch. tomentosa is divided into two forms — f. marina (sive murida)
and f. stagnalis (s. incriistata), the latter with the synonvme Ch.
cera-tophylla Wallr., which name is employed most frequently in Central
Europé. It is onlv Ihe presence of Ihe species in fresh limy water and
the accompanying lime covering of Ihe stern giving the species a
dis-figured habitus, I hat caused Ihe dislinclion of f. stagnalis. The keeping
apart of the two forms liave proved to cause a misleading
interpretation of the character of the localities. Hetween the two forms all
Iransi-tions are to be found and specimens from one and the same locality
cail be verv different with regan| to the linie covering and the
growth. This is particularly Ihe case of some bays or coves separated
from the sea and situated in limy districls, and with the sea-water
running in during some linie of Ihe vear. Snch a locality is Bogeviken
at the east coast of Golland and so were some localities at Stockholm
and Gefle. From Skälsö (Gotland) and Hummelfjärden at Öregrund
(Uppland) the specimens are obviously »f. incrustata*, though these
places are connected with I lie sea and the same effect seenis to be
present at some localities in Åland. — Verv interesting in this question
is the Lake of Tingstäde träsk (Gotland), which locality Hasslow (1931,
p. 116) includes aniong the localities of Ch. lomentosu 1. marina. This
lake is situated 45 ni above the sea-level in a limy dislrict |see
Lundqvist 1925, i). 88). The specimens examined by Hasslow onlv show
a slight linie covering, which may explain the mistake, il Ihe locality
bas not been conlrolled ön a map. Lundqvist (pp. 94—96) gives
an explanation of the slight linie covering of the C7i«/-r<-species in
some parts of the lake, wlieii lie discusses Ihe question of the
formation of the lileach-banks as due lo the wiiid-currents. Ön Ihe
nortli-western sides of these banks, which are exposed lo the currents, Ihe
C7if/rf(-vegelation is sparse and Ihe specimens are without Ihe felty crust
of linie, hut the sheltered slopes of the banks show a lliick and
lime-incrusted C/iara-vegetation. Dr B. Pettersson has also called my
atten-tion to Ihis fact and has kindly placed to my disposai bis material of
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