Researches on the morphogenesis of the genus Peyssonnelia Decaisne. — This paper reports the first result on morphogenetic researches in cultures of 3 species of the genusPeyssonneliaDecne. The development ofPeyssonnelia rubra(Grev.) J. Ag. is of «Dumontia type »(CHEMIN, 1937) that one ofPeyssonnelia squamaria(Gmelin) Decne. and ofPeyssonnelia inamoenaPilger of «Naccaria type». According to our cultures results the morphogenesis of genusPeyssonneliais of two type. Sample ofP. squamariaandP. inamoenaare collected in the gulf of Trieste (Nord Adriatic Sea) those of P. cfr.rubrain the Morlaix Bay (English Channel). Taxonomic value of the results are discussed.