Abstract. C19H1404, monoclinic, P2,/c, a= 15.32 (2), b= 7.59 (1), c= 13.16 (2) A, fl= 80.7 (8), Z= 4, U= 1509 A3, Dc= 1.35 Mg m-3, g= 0.1079 mm-', R= 0.068 for 1204 reflexions [I> 3a (I)! and 236 parameters. The fl-naphthyloxy group is axial to the B ring which has an envelope conformation.