MARINE ALGAL VEGETATION 137 



Delesseria alata, Acrosiphonia, Polysiphonia urceolata, Plnmaria elegans 

 and Rhodymenia palmata occur. Porphyra umbilicalis occurs as an 

 epiphyte in the Vestmannaeyjar, and also Cystoclonium, Polysiphonia 

 urceolata and others. 



The Gigartina-be\i is very luxuriant in the Vestmannaeyjar and 

 at Ondver5arnes; it may be said to be, on the whole, luxuriant in 

 S. and SW. Iceland. As regards the relations between Gigartina and 

 Corallina, the following observation from the Vestmannaeyjar may 

 be recorded. At Brimsur6, on the south-east side of the inhabited 

 island, where the littoral zone consisted of large, although not par- 

 ticularly high boulders, these were entirely covered above by a 



V V V 



dense GzV/ar/z/?a-vegetation, while Corallina formed just as dense a 

 belt around them below. 



Chondrus crisp us also grows socially in S. and SW. Iceland. 

 It is true that Chondreta of lesser extent occur usually at or near 

 low-water mark , but nowhere does the species occur nearly as 

 luxuriantly as does Gigartina. The C/zonrfriis-vegetation is most 

 luxuriant in the Vestmannaeyjar and at Eyrarbakki. Between the 

 skerries off the latter place, the broad-fronded form grew in abun- 

 dance, both above and a little below the limit of low-tide. In both 

 the places mentioned, which belong to S. Iceland, it grows in such 

 abundance that the vegetation might almost be termed an associa- 

 tion; in SW. Iceland on the other hand, it seems to occur more 

 sparsely, and the small Chondreta may then be considered to be- 

 long to the Gz</a/'/zna-association. 



Ahnfeltietum. Ahnfeltia plicata grows socially in S. and SW. 

 Iceland and usually forms a narrow belt at and below the limit of 

 low-tide. The individuals are very frequently matted together by 

 the byssal threads of various small molluscs, and worms and quan- 

 tities of snails are found between the plants. In reality this vege- 

 tation is more nearly related to the Cofa//ina-association than to 

 the GzV/ar/zna-association. This species grows also scattered among 

 Corallina and Gigartina. 



The intermingled species are only few in number, for example, 

 Ralfsia densta which may occur abundantly in small depressions, 

 and Leathesia difformis which sometimes occurs in abundance as 

 an epiphyte. Ahnfeltia is most frequently decoloured above low- 

 water mark. 



Chsetomorpha Melagonium occurs rather frequently, grow- 



