.11 ill AN KI^ER. fSF.C. ARCT. EXT. I HAM 



I'urii). Psamtnosteus migrated iii Middle Devonian age to the hrackish 

 water lak particularly tho-i- of the south-eastern part of the 



north Atlantic mainland, and thence lo the fiv.-h water lakes. During 

 the Middle Devonian one form in this manner penetrated into the 

 north of Scotland. In the lower part of the Upper Devonian it extended 

 little hy little along the northern part of the north Atlantic mainland 

 right up to the eastern part of the recent Arctic Archipelago of North 

 America, \\hich pre-nniahly formed the north-western border of that vast 

 continent. 



The line of this Arctic extension appears to have 

 played the most significant part in the formation of the 

 fi.-h fauna that are descrihed in the present work. 



I'rini.-.l M.-.I-.-II -2. I'.M:,. 



