  Let $N_{g,n}$ be an $n$--punctured non--orientable surface of genus $g$ with
one boundary component. For $g\geq 2$ one of the generators of the mapping
class group of $N_{g,n}$ is a crosscap transposition. We give explicit formulae
for the action of crosscap transpositions and their inverses on the set of
multicurves in $N_{g,n}$ in terms of generalized Dynnikov coordinates.
