In the title compound, C(32)H(28), the central cyclo-octa-tetra-ene ring has a boat conformation, and the mol-ecule is saddle shaped. The seat is defined by the mean plane of the four-atom attachment points (r.m.s. deviation = 0.014 Å) of the two bicyclo-heptenyl substituents. These substituents comprise the pommel and cantle, with each mean plane defined by four atoms proximate to the seat (r.m.s. deviations = 0.002 and 0.004 Å). Relative to the seat, the pommel and cantle bend up 31.16 (4) and 29.40 (5)°, while the benzo units (flaps, r.m.s. deviations = 0.006 and 0.009 Å) bend down 36.75 (4) and 38.46 (4)°. The mean planes of the dimethyl-ethyl-idene units are almost perpendicular to the saddle seat, making dihedral angles 86.89 (4) and 88.01 (4)°.