  Let $X$ be an affine surface admitting a unique affine ruling and a $\mathbb
C^*$-action. Assume that the ruling has a unique degenerate fibre and that this
fibre is irreducible. In this paper we give a short proof of the following
result of Miyanishi and Masuda: the universal covering of $X$ is a hypersurface
in the affine 3-space given by the equation $x^my=z^d-1$, where $m>1$.
