Left: schematic representation of the mode labeling/quantum numbers used for island modes. Right: illustration of the relation between the quantum numbers of spherical and island modes. The quantum number n is the number of nodes in the longitudinal direction of the island mode (along the ray γ), ℓ is the number of nodes in the transverse direction of the mode (transverse to γ) and m is the number of azimuthal nodes. n_s, ℓ_s and m_s are the quantum numbers of spherical modes. In the right figure, the multiplets of island modes correspond to diagonal colored bands, whereas the multiplets of spherical modes would have the form of vertical bands. The plotted mode on the left corresponds to n = 46, ℓ = 1 and m = 0. (This figure is available in color in the electronic form.)