  The model, introduced in a previous paper, for the description of the
octupole and quadrupole degrees of freedom in conditions close to the axial
symmetry, is applied to situations of shape phase transitions where the
quadrupole amplitude can reach zero. The transitional nuclei 224,226Ra and
224Th are discussed in the frame of this model. Their level schemes can be
reasonably accounted for assuming a square-well potential in two dimensions.
Electromagnetic transition amplitudes are also evaluated and compared with
existing experimental data.
