C20H15Cl, M(r) = 290.8, monoclinic, P2(1)/c, a = 20.449 (4), b = 11.473 (2), c = 13.025 (2) A, beta = 108.91 (1)degree, V = 2890.9 A, Z = 8, Dx = 1.336 g cm-3, lambda (Cu K alpha) = 1.5418 A, mu = 21.14 cm-1, F(000) = 1216, T = 294 K, R = 0.045, wR = 0.049, for 3471 diffractometer data [Io > or = 3 sigma (I)]. The ring system is puckered as a result of the bulkiness of the 12-methyl group.