1908] Decapod Crustaceans. 53 
winter, it is caught from January to March at 40—50 fathoms, 
and may even be taken in large quaniities in water no deeper than 
20 fathoms. 
The period when Pandalus makes for shallower loealities hap- 
pens to ceoineide with the time of casting its spawn, and it is chiefly 
then too that it repairs to the Drammen Fiord. It seems certain 
that large numbers seek shallower water about the time when the 
spawn is to be hatehed; and we know, in any case, that they prac- 
tically disappear from places where they were previously found in 
abundance, and subsequently return to them again. Whether or not 
Pandalus undertakes other *wanderings” in addition to those from 
the deeper to the shallower portions of the fiord, I am unable to 
say. However in the Drammen Fiord this change from one depth 
to another assumes the character of å regular migration into and 
out of the fiord, seeing that the shallower parts, over say 40 fathoms, 
afford the prawns å suitable temporary residence during the spawning- 
time, whereas the deeper portions which they prefer at other times 
are unsuitable owing to their hydrographical conditions. It is for 
this reason that the prawns move out of the fiord again when they 
wish to repair to deeper water. 
No doubt we do find Pandalus in the Drammen Fiord during 
the summer also at åa depth of about 30—40 fathoms. Still as å 
øeneral rule the bulk are not found there till well on in the winter 
and in the spring. 
Investigations have been carried on in the Christiania Fiord 
into the regular wanderings of Pandalus at certain definite seasons 
of the year, from åa bathymetric point of view. Å natural reason 
for these removals seems to be the regular hydrographical changes 
that take place in the fiord during the winter months, that is to 
say the very time of year when Pandalus borealis desires to frequent 
shallower water. 
The layer in which Pandalus borealis appears generally to reside 
has å low temperature of about 69 C. and å salinity of about 34— 
35 %0. In the Skagerack we get water of this temperature and 
salinity under the surface layer, and above the salter water presum- 
ably of Atlantic origin which fills the deeper portions of that sea. 
In these deeper portions P. borealis is not found, though on the other 
hand it is met with right away down to the mouth of the Kattegat 
at all depths where the above-mentioned layer of water prevails. 
It similarly oceurs in all fiords along both sides of the Skagerack, 
