def _check_triangular_bounds(self, var, coords=None, axis='x', nans=None):
        """
        Checks whether the bounds in the variable attribute are triangular

        Parameters
        ----------
        %(CFDecoder.get_cell_node_coord.parameters)s

        Returns
        -------
        bool or None
            True, if unstructered, None if it could not be determined
        xarray.Coordinate or None
            the bounds corrdinate (if existent)"""
        # !!! WILL BE REMOVED IN THE NEAR FUTURE! !!!
        bounds = self.get_cell_node_coord(var, coords, axis=axis,
                                              nans=nans)
        if bounds is not None:
            return bounds.shape[-1] == 3, bounds
        else:
            return None, None