  In 1995 Doebner and Mann introduced an approach to the ray representations of
the Galilei group in ($1+1$)-dimensions, giving rise to quantum generators with
an explicit dependence on time. Recently (2004) Wawrzycki proposed a
generalization of Bargmann's theory: in his paper he introduce phase exponents
that are explicitely dependent by 4-space point. In order to find applications
of such generalization, we extend the approach of Doebner and Mann to higher
dimensions: as a result, we determine the generators of the ray representation
in ($2+1$) and ($3+1$) dimensions. The differences of the outcoming formal
apparatus with respect to the smaller dimension case are established.
