F. Borgesen: General remarks. 489 



St. Jan. The components of the West Indian algal communtiy 

 consisted of Enteromorpha plumosa, Chætomorpha and Rhizo- 

 donium-species, Pylaiella fulvescens etc., all thread-like algæ. 



In crevices in rocks and in small caves, especially in rather 

 shady places, several small algæ are able to grow a little above 

 the surface of the sea, so they may become rather dry when the 

 sea is calm. In such places in Store Nordside Bay (.Magens Bay), 

 St. Thomas, a vegetation was found uppermost composed of 

 Bosinjchia tenella, together with several Myxophyceæ, Chætomorpha 

 antennina, Ch. hrachygona and other forms, Struvea delicatula, 

 Hypnea spinella^ Centroceras claviilatum, Sphacelaria tribiiloides and 

 fiircigera, Tænioma perpusillum, Wrangelia Argus, Enteromorpha 

 pliimosa, Polysiphonia ferulacea, Ectocarpus etc. But the great 

 number of these species are yet, for the most time, covered 

 by the sea, living quite near the surface. The rocks washed by 

 the spray from the sea were covered by crusts of various Lichens^) 

 and below Ralfsia expansa and Lithothamnion were found inter- 

 mingled with the Lichens. 



Upon stones and shells in somewhat exposed places crust- 

 like algæ are often found in shallow water, for instance Ralfsia 

 expansa, Hildenbrandia prototypus, Peyssonnelia etc. And upon 

 stones scattered on sandy bottom in more sheltered places in shal- 

 low water Agardhiella tenera, Castagnea Zosteræ, Rosenvingea 

 Sanctæ Criicis, Ectocarpus, Hypnea musciformis, Spyridia fila- 

 mentosa, Gratelou pia etc. grow in larger and smaller tufts. 



Upon rocky and stony coasts often in bays, but also in rather 

 exposed localities Sargassum and Turbinaria form together an often 

 luxuriant vegetation, exactly corresponding with the Fucaceous 

 vegetation of the Northern seas. 



A characteristic algal vegetation occurs on piers and rocks, 

 over which the waves are rolling, for instance in the inner harbour 

 of St. Thomas where the water was much polluted. The most 



^) According to the determination of Wainio, I collected here: Pannelia 

 lusitana Nyl. var. decipiens Wain., Pertusaria prætervisa Wain., Placo- 

 dium Boergesenii Wain., var. squamosa areolata Wain., Placodium di- 

 placium (Ach.) Wain.; Physcia integrata Nyl., Physcia picta (Sw.) Nyl.; 

 Rinodina pyxinoides Wain. ; Buellia conspiraiis Nyl., Buellia orcularia 

 Wain.; Heppia Bolanderi (Tuck.) Wain.; Collema acarosporoides Wain.; 

 Synalissa lichinella Wain.; Pyrenopsis negans Wain.; Psorotichia Boer- 

 gesenii Wain. 



