The solution of generalised spheroidal wave equations which result from the Schrodinger equation for a hydrogenic system in half space by separation of variables in prolate spheroidal coordinates (ξ, η, φ) is reexamined. Alternative expansions for the solutions to the η-equation are derived. The expansions are explicitly of odd parity. With such a naturally inherent desired property they can be employed directly in the truncated matrix method in calculating the eigensolutions and will consequently considerably facilitate numerical work. The odd-parity eigenfunctions in their new forms are shown to be convergent in the interval -1 ≤ η ≤ 1.