54 Alf Wollebæk. [No. 12 
where the entrance barrier at the mouth is not of such å height as 
to preclude new water of the said character from slipping over. 
Such fiords are the Gullmar Fiord in Bohuslån, the Christiania Fiord, 
the Brevik and Langesund fiords and å number of others along the 
Norse coast. 
There are several fiords along the coast where the depth-eondi- 
tions might lead one to suppose that Pandalus borealis would be 
met with, but where nevertheless none are to be found. 'The sole 
reason for this is that the fiords are too shallow at the outlets, or 
in other words that their barriers are high enough to prevent the 
water-layer appropriate to the species from entering. As examples 
of such stagnant fiords we may mention Kilsfjord near Kragerø and 
Frierfjord near Brevik, both of which are continuations of long fiord- 
arms. Immediately outside the barriers of both Kilsfjord and Frier- 
fjord, in the Kragerø channel and in the Brevik fiord, we find num- 
bers of Pandalus borealis occurring, notwithstanding that the ordinary 
depth-conditions are not materially different from the deeper portions 
of the fiord that lies within. But in this case the appropriate water- 
layer referred to is not prevented by a too-high barrier from entering 
the outer portions of these fiord-arms. 
As the varying oceurrence of Pandalus borealis regarded from 
a bathymetric point of view is best known from the Christiania Fiord, 
and as moreover in hydrographie respects this fiord has been more 
thoroughly investigated than any other we shall select it now as an 
example. 
To better understand this fiord's hydrographic conditions, the 
changes in which are supposed to be the cause of the varying oceur- 
rence of Pandalus borealis at different seasons, it is necessary first 
briefly to deseribe the configuration of its bottom. 
Like most of the Norse fiords the Christiania Fiord at its outlet 
is partly separated from the sea by å submarine ridge or barrier. 
There is one of these barriers at Færder, 40 fathoms below the 
surface: within it the depth is 150 fathoms. At Drøbak there is . 
another barrier 30 fathoms below the surface, inside of which in the 
Christiania Fiord's inner basin the depth is over 60 fathoms. Finally 
between Næsodden and Snarøen the Bundefjord, which is about 90 
fathoms deep, is separated from the rest of the fiord by å barrier 
30 fathoms below the surface. 
All these barriers cooperate to cause the salter water which 
streams in from the sea in the winter, and which being heavier than 
