  This paper constructs a bijection between irreducible $k$-shapes and
surjective pistols of height $k-1$, which carries the "free $k$-sites" to the
fixed points of surjective pistols. The bijection confirms a conjecture of
Hivert and Mallet (FPSAC 2011) that the number of irreducible $k$-shape is
counted by the Genocchi number $G_{2k}$.
