488 



stones more or less abundantly 1 ). In additions to Caulerpa 

 many other algae are characteristic of such localities; of the 

 Chlorophycese we find for instance Dictyosphseria favulosa and 

 D. van Bossese, Valonia ventricosa, V. utricularis and V. ma- 

 crophysa all forming smaller or larger crust-like bodies, also Cla- 

 dophoropsis membranacea occurs fixed as well as detached form- 

 ing sEgagropila-]ike bodies upon the bottom. And these are joined 

 with Chamxdoris annulata, Halimeda Opuntia and H. incrassata, 

 Penicillus and many others. Of Phae.ophycese we most frequently 

 find several Padina- and Dictyota-species, tufts of Ectocarpus, 

 Colpomenia and Hydroclathrus etc. and finally many Rhodo- 

 phycese, of which the most characteristic are Gelidiopsis rigida, 

 Bryothamnion triangulare, Digenea simplex, Lauren da papillosa, 

 Hijpnea- and Spyridia-ioTins, Galaxaura, Amphiroa fragilissiwa 

 and other corallinaceous alga?, Centroceras and many other species, 

 all forming larger or smaller tufts often intermingled between 

 each other. 



Upon the very exposed rocky coast of the northwest side 

 of St. Groix several alga? occur so high above the sea-level that 

 they are moistened only by the spray. Uppermost were found 

 several Myxophycess and small tufts of Laurenda obtusa and 

 L. papillosa, of Dilophus guineensis, Dictyota ciliata and Padina 

 gymnospora. Amongst these, scattered tufts of Chsetomorpha an- 

 tennina were found in abundance and lower down Polysiphonia 

 ferulacea, Centroceras clavulatum and Ectocarpus breviarticulatiis. Ex- 

 tensive patches are formed by Aglaozonia canariensis, which covers 

 the very uneven rocks with its fleshy - - cartilaginous red-brown 

 thallus; now and then Ralfsia expansa and Lithothamnion, too, 

 form smaller or larger crusts. This association can perhaps be 

 compared with that of Callithamnion arbuscula at the Faeroes, 

 the tropical association like the northern one living in such ex- 

 posed places upon steep rocks where it is exposed. to the whole 

 force of the sea, and some of the tropical algaa, too, being able 

 to retain the water like small sponges. 



Another characteristic association of alga?, corresponding to 

 the Bangia /ros/?ora-association of the Faeroes was found in 

 rather exposed places upon the steep rocky coast at Cruz Bay, 



J ) BORGESEN, F., An ecolog. and system, account of the Caulerpas, 1. c. 

 p. 346. 



