34 Sigurd Johnsen. 
ranean whose waters then most probably did not attain the high 
values of temperature and salinity of today. The Mediterranean 
thus may have harboured some boreo-Atlantic forms, pelagic as 
well as coastal fishes. When the boundaries receded northwards 
some forms may have remained, adapting themselves to the new 
conditions. As far as I know the relict theory has not hitherto 
been applied on the marine fauna of the Mediterranean, but only 
for some of the fresh-water lakes of Central and Southern Europe. 
As already stated (on p. 21) I think it safe to conclude from 
the present data that M. glaciale has a discontinuous range and 
that the negative data from the Atlantic to the south of abt. 40°N. 
are not due to deficient investigations of these waters. The hydro- 
graphical data tend to corroborate this. On the northern route © 
of the “Michael Sars” Expedition in 1910 from Newfoundland to 
Ireland M. glaciale was caught on all the stations where pelagical 
fishing was undertaken. The fig.99 in Murray & Hjort (1912) 
represents a hydrographical section of the Atlantic along this route. 
The surface layers down to 100—200 metres have a salinity of 35.5 °/o0 
and ate followed by a vast layer where the salinity is 35.0 °/oo, 
in the eastern Atlantic down to 1500 metres depth. The tem- 
perature was abt. 14° C. at the surface and 10° in 500 metres. 
The fig. 63 in the work mentioned represents a hydrographical 
section from the coast of Africa to the Azores, an area where 
M. glaciale is wanting. Here the salinity is 36.5—36.0 °/oo down 
to 500 metres, the isohaline 35.5 °/oo is met with in 700 metres 
depth and 35.25 °/oo in 1500 metres; the temperature is 20° C. 
at the surface and 13° at 500 metres depth. The distribution of 
M. glaciale in the Atlantic coincides remarkly well with that of 
the Gulf Stream, not only acros the Atlantic but also in northern 
latitudes where branches of that current enter the Arctic waters. 
The warm and salt water of the Central Atlantic seems, however, 
to act as a barrier to the progress of the species further south.*) 
1) Meisenheimer (1906) has tried to give a zoogeographical classi- 
fication in regions of the pelagic organisms based upon the distribution of 
the Pteropods. His region “Nordatlantisches Ubergangsgebiet” is that of the 
Gulf Stream; the southern boundary of this zone towards the circumtropical 
zone is running from the American coast at abt. 33° N. across the Atlantic 
to Cap Finisterre. The North Atlantic does not seem to harbour many pelagic . 
fish peculiar to this area. Besides M. glaciale I shall mention M. arcticum, 
known from the waters of Greenland, Iceland and Ireland; Bathylagus bene- 
dicti and B. euryops taken off the Atlantic coast of N. America and off the 
coast of Ireland; these species were all captured by the “Armauer Hansen” 
in the Atlantic at abt. 55° N. 
