797 



chæte ferox, Cladophora nipestris, '-'C. sericea, Pledonema norvegiciim 

 and "Spiriilina subsalsa. If we add these to the above-mentioned 

 number\ ^Ye have 143 species. Of Ihese, 111 are also found at 

 the Færoes. Thiis North-East Iceland has 23 species less in com- 

 mon with the Færoes than South -West Iceland. 



Firstly, as to the 32 species found at North- East Iceland and 

 not at the Færoes, they may be divided into the following groups: 



I. The A ret i c gro up: Turner ella Pennyi, Delesseria Baerii, Po- 

 hjsiphonia arctica, Lithothamnion flavescens, L. foeciindiim, Om- 

 phalophylliim ulvaceiim, Dictyosiphon corymbosiim, Laminaria 

 nigripes and Monostroma groenlandiciim; 9 species in all. 

 II. The Su baret i c gro up: 



Subdivision 1: Peyssonnelia Rosenvingii, Lithothamnion tophi- 

 forme, Ralfsia densta, R. ovata, Coiledesme hulligera, Saccorhiza 

 derniatodea, Ulothrix snbflaccida , Pseiidendocloninm marinum, 

 Urospora Hartzii, Acrosiphonia penicilliformis ; 10 species in all. 

 Subdivision 2: Phæostroma pustalosnm, Chlorochytrinm derma- 

 tocolax; 2 species in all. 



III. The Boreal-arctic group: Chantransia microscopica. 



IV. The Cold-boreal group: Petrocelis Hennedyi, Lilhothamnion 

 norvegicnm, Ascocyclns islandicns, Ectocarpus penicillatus, Spha- 

 celaria radicans, Dictyosiphon Mesogloia, D. Chordaria, Entero- 

 morpha aureola, Ochlochæte ferox, Pledonema norvegicnm; 10 

 species in all. 



If we compare these species with those that are not common 

 to South -West Iceland and the Færoes, we at once perceive a very 

 distinct difference in that the arctic group is much increased^. 

 It is not likely that any of these 9 species will be found at the 

 Færoes: and as to the subarctic species of the subdivision 1, it is 

 likewise improbable that they will be found there, a few species 

 perhaps excepted. On the other hånd the species of subdivision 2 

 may probably also be found on the Færoese coasts, and this is cer- 

 tainly also the case with the greater part of the cold-boreal species. 



^ It is, however, doubtful, whether they may all be found at North and East 

 Iceland proper; the 8 species marked with asterics and which have all been found 

 much farther north, for instance at Greenland, must, however, be supposed to occur 

 at North Iceland, and especially at East Iceland. 



' This group will most probably be still more increased on renewed inve- 

 stigations, as we may certainly suppose, that the two arctic species at an3' rate, 

 Cruoria arctica and Ceratocolax Hartzii, found at the other side of Hornbjarg, also 

 grow there. 



51* 



