26 Hjalmar OstergTen. [Xo. 9 



Jæ?As. Nowhere in Nonvav the Holothurian fauna is purely arctic, 

 hardly preponderantly arctic, unless perhaps in East Finmark. 



The purely arctic fauna beg-ins, as regards the Holothurians, 

 first farther to the east and farther to the north. The chmatic 

 factors which cause this alteration, are Avithout doubt the drift-ice 

 and the low bottom temperature of 0° C. The limit of the drift-ice 

 and the limit of the „cold area" are subject to displacements in eonse- 

 quence of which the limit of the purely arctic fauna is liable to 

 small changes from year to year. The pelagic larvæ of the boreal 

 species are carried by the Gulf Stream towards the north, and can 

 probably during favourable years be developed in places, wliich lie 

 outside their natural district. Solitary occurrences in Barents Sea, 

 or on the west coast of Spitzbergen, of a species, which else is not 

 known in the purely arctic region, does not therefore give us any 

 right, according to my opinion, to regard that species as a normal 

 component of the arctic fauna. 



The sea fauna in the greater depths in the AVest Fiord and 

 some of the adjoining fiords and sounds is almost entirely boreal. 

 But otherwise the Norwegian coast north of the Arctic circle betongs 

 in faunistic respect to the transitional zone between the Boreal and 

 Arctic regions. Should an attempt be made to draw up a definite 

 boundary line between the Arctic and Boreal regions, this line 

 would have to be drawn through the intermediate or transitional 

 zone, and go through places where the arctic and boreal species 

 balance each other. In drawing this boundary line, all isolated 

 occurrences in localities, differing in hydrographical respect, must 

 not be tåken into account. 



As far as the Holothurians are concerned, the Avhole of the 

 west coast right up to the North Gape (71*^ 10' N.) betongs then to 

 the boreal region. In East Finmark the Holothurian fauna is as 

 yet too little known that we may be able with full certainty to decide, 

 whether it is preponderantly boreal or arctic. If we for the present 

 put the limit at the North Cape, we shall find that there are three 

 arctic species which go a little into the region of the boreal fauna: 

 Chiriclota lævis, Myriotroclius rinJiii and Trochostoma horecde. The 

 two latter appear, however, only in fiords with low bottom tempera- 

 ture. Boreal species which go a little into the region of the arctic 

 fauna are at least two : Stichopus tremukis and Labidoplax busli. 

 According to statements in literature on the subject, there are three 



