In the title compound the two five-membered rings are cis connected. T
he torsion angle C(1)-C(8a)-C(3a)-C(3) about the bond common to the tw
o five-membered rings is unexpectedly large, 26.7 (3)-degrees. The ang
le formed by the least-squares plane of the indene subunit with the le
ast-squares plane of the terminal cyclopentane ring is 67.7 (1)-degree
s.