14 G-. 0. Sårs. [No. 4 



salt water at a very uniform, and in some cases exceedingly high, 

 point, amounting, according to the statements of Dr. Gkan, during 

 the summer-months to no less than -f- 30° C. Even in the winter, 

 when the surface of the beds is covered with ice, the temperature 

 of the water at some distance below the ice is found to be unu- 

 sually high, being in some cases stated to be + 10° C. It is 

 indeed this high and uniform temperature, and perhaps also the 

 chemical composition of the water, that in such a remarkable manner 

 favours the great productiveness of the parent oysters in some of 

 these beds; and it is possible that the occurrence of the present 

 peculiar Calanoid may also find its explanation in the same excep- 

 tional physical conditions. 



There is abundant cvidence for the assumption that the marine 

 fauna of Norway has been subjected to great changes during past 

 ages, in accordance with the changes in the climate and other phy- 

 sical conditions, and that of course a repeated emigration and immi- 

 gration of species has tåken place. Thus, at a rather remote epoch, 

 the so-called glacial period, the fauna exhibited everywhere off our 

 coasts a pronouncedly arctic character, as shown by the fossil shells 

 contained in the glacial beds, and also by the so-called relict forms 

 still living in the great deeps of our fjords, and even in some of 

 our lakes. This period was followed by another, in which a great 

 change of climate occurred, the mean temperature of the year having 

 in all probability been considerably higher than it is at present; 

 and during this period, while a boreal fauna replacecl the arctic 

 one, an immigration of some pronouncedly southern forms also 

 seems to have tåken place. In the subsequent change in the climate, 

 these latter forms for the most part again disappeared, or retired 

 to more southern latitudes, leaving only very slight traces of their 

 presence in the recent Norwegian fauna. It is, however, very likely 

 that in certain exceptional cases some few of these southern forms 

 may have been able to survive in higher latitudes — a survival 

 analogous to that of the above-mentioned relict arctic forms - — , 

 and that the present Calanoid ought to be regarded as an isolated 

 remnant of a previous fauna different from that now existing on 

 our coasts, its southern origin being not only proved by its luxuriant 

 development in the warm water of the oyster-beds, but also by its 

 very near relationship to the tropical species recorded by Th. Scott 

 from the Gulf of Guinea. 



