Shells are often observed around elliptical galaxies (Malin & Carter 1983). Stars in the shells can be regarded as test particles. Therefore for a simple shell morphology (Hernquist & Quinn 1985) the distances between shells allow one to trace the shape of the potential of the host galaxy (Quinn 1984). One can also deduce the distribution of gravitating material. Following this method one concludes that the distribution of luminous matter alone cannot account for the observed shell structure. Depending on the age of the outermost shell one can conclude that either the massive halo terminates at a radius ≃ 5 re ≃ 15 kpc., or that the core of the halo γ≃2.5 kpc, where the halo density is given by ρ≃ {r2 + γ2}−1. In either case, the central density of the halo is no less than an order of magnitude in excess of that expected for a spiral galaxy of comparable luminosity (Figure 1.).