Subject to rules prescribed by the board, any member may elect to contribute at rates in excess of those provided for in this chapter for the purpose of providing additional benefits. Benefits provided by this chapter shall be exclusive of such additional benefits. The exercise of this privilege by a member shall not require the city to make additional contributions on behalf of such member. The provisions of Section 2.124.1880 of this chapter shall apply also to additional contributions. The board, upon request, shall furnish to such member information concerning the nature and amount of additional benefits to be provided by such additional contributions. (Prior code § 34.11.1103)