52 JOHAN KI^ER. [SEC. ARCT. EXP. FRAM 



which this rapacious creature presumably could crush the cranial and 

 osseous plates of the armoured fishes. 



Glyptolepis, which with Holoptychius forms appear to have been 

 quite common in these regions, was closely related to the above. The 

 latter were fishes of a less powerful build, with more slender teeth and 

 round, thin scales of enamel. 



Finally, certain small Osteolepis forms appear also to have lived 

 there. They were powerful rapacious creatures, not exceeding about 

 2030 cm. in length. 



The fishes which I have described confirms the opinion which I have 

 already put forward, that the fossiliferous strata at Skrap Valley were 

 deposited in a large brackish lake, possibly an estuary in which marine 

 and fresh water fishes met. 



The tiny mussel, Phtonia, entered from the sea, adapted itself to 

 altered conditions of existence, and multiplied in huge quantities. Some 

 of the fishes, particularly the Holoptychius forms also indicate a free 

 connection with the sea, for their remains are found both in purely 

 continental formations (lake and river deposits) and in marine sediments; 

 it is therefore natural to assume that like several forms of the present 

 time, these creatures migrated from the sea to the rivers. This is also 

 indicated by their wide extent over the whole of the northern hemisphere 

 in closely related forms. 



Other forms appearing, however, were presumably genuine fresh 

 water fishes, which like many of the recent forms were able to adapt 

 themselves to the life in brackish lakes. This feature concerns possibly 

 f-ilyptolepis, but especially Osteolepis, Psammostens, and Bothriolepis. 



There is however one point that I desire to emphasise. It is not 

 proved that a fishes has lived in a brackish water lake because we find 

 its remains in the sediment. The river or rivers that flowed through 

 such a region may have carried the body with it and deposited it in a 

 different habitat. In such cases there will always be a certain amount 

 of uncertainty. 



The other fossiliferous horizons that are to be found higher up in the 

 series present a different aspect to that of the abundant fish horizon of 

 Skrap Valley. None of them show traces of marine mussels, and the 

 fishes of which we find remains are of such a character that we must 

 assume them to pure fresh-water forms. 



In the dark schists of Galgeodden with remains of plants, which 

 appear to be quite local in appearance, we find simply the small 

 Bothriolepis and a scale of Glijptolepis. At S. 0. Haken there are only 



