Preliminary studies on the marine phythobenthic communities in the Straits of Sicily and adjacent islands. — The results of algological researches carried out by the Gruppo di Algologia of the S.B.I. in the Straits of Sicily and adjacent islands are reported. 288 species have been collected, 275 of which have been identified: 160 wereRhodophyta, 62 Phaeophyta, 32 Chlorophyta, 16 Cyanophytaand2 Angiospermae. The vegetational research leads to the following conclusions: 1 - the harbour areas (Pantelleria, Malta: loc. 1 and 11) show a nitrophile vegetation, particulary near La Valletta where an almost pure population ofPterocladia pinnatais found; 2 - there are important biogeographical differences between Pelagie islands (Lampedusa, Linosa) and Pantelleria. In fact the former ones have an algal flora composed mostly of eastern mediterranean species, whilst the latter shows strong affinities with the north-african basin, as is demonstrated by the rich well developed belt ofCystoseira sedoides; 3 - several species of atlantic origin, such asCallophyllis laciniata, Peyssonnelia coriacea, P. inamoenaandCastagnea chordariaeformis, have been found on the banks (loc. 3, 6, 7).