Résumé : 13‐epi‐9‐desacetylxenicin (2), isoxeniolide‐A (3) and 7, 8‐oxido‐isoxeniolide‐A (4), three novel nine‐membered diterpenoids have been isolated from the alcyonarian Xenia novae‐britanniae. Their structures have been established on the basis of their spectral properties. Structure 2 has been confirmed by X‐ray diffraction analysis. Copyright © 1979 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim