10 M. FOSLIE. [1905 



which greatly impedes the limitation of the species. Therefore, 

 several of such forms are rather to be considered as occasional 

 and accidental variations than as true varieties in the usual sense. 

 Another fact contributing to the difficulty of limitation is the great 

 mutual uniformity of anatomical structure prevailing particularly in 

 the species of the genera belonging to the group of the Litlio- 

 thamnioneoe. This is less the case in the group of the Melobesiese, 

 e. g. Lithophyllum, which is chiefly represented in the tropical or 

 subtropical areas. Besides, the forms belonging to the former group 

 are most richly fructiferous at a rather young stage, whereas old 

 specimens, especially of branching species, are almost always ste- 

 rile, though still continuing their vegetative development. 



It is, however, possible that there are forms of some species 

 which are to be properly looked upon as relics from a period 

 when the glacial formation had a greater extent to the south than 

 in our days. This may perhaps be the case with e. g. Lithotham- 

 nion glaciale f. Granii, such as this form occurs peculiarly in the 

 Christianiafjord, in the Cattegat, and even farther to the south at 

 the coasts of Denmark. On the other hand, the development and 

 rather numerous occurrence of this form in the said areas seem 

 to tell against such a view. The occurrence of the species at the 

 coast of Ireland seems more to favour the notion of a relic. It is, 

 however, as yet difficult to decide this, as the species, in unfavou- 

 rable local conditions, often assumes similar forms even in the 

 arctic and subarctic areas, and the continuity of the distribution 

 and of the development of the forms is still too little known. 

 There are also other arctic or subarctic species, with smaller area 

 of distribution, which occur to the south in forms which may be 

 looked upon as relics. 



In the sequel I will give a survey of the species occurring at 

 the coast of Norway, and of their geographical distribution with 

 the limitation which will be in all essentials my final view of the 

 mutual relations of these species. I will, however, deal with all 

 the forms hitherto described of the species, even if they are not 

 all found within the said area. All the species or forms will be 



