  A gamma-rigid version (with gamma=0) of the X(5) critical point symmetry is
constructed. The model, to be called X(3) since it is proved to contain three
degrees of freedom, utilizes an infinite well potential, is based on exact
separation of variables, and leads to parameter free (up to overall scale
factors) predictions for spectra and B(E2) transition rates, which are in good
agreement with existing experimental data for 172-Os and 186-Pt. An unexpected
similarity of the first beta bands of the X(5) nuclei 150-Nd, 152-Sm, 154-Gd,
and 156-Dy to the X(3) predictions is observed.
