For an arbitrary parabolic
subgroup P of the real or complex symplectic group, let N be the nilradical. Using
Kirillov theory, a subset of the dual of N is found, whose complement has Plancherel
measure zero. It is shown how these representations extend by combining with the
oscillator representation of a lower rank symplectic group. A result is obtained
concerning the commuting algebra of the restrictions to P of the principal series
representation of the symplectic group induced from a unitary character of the
opposite parabolic.