(a) The board of trustees shall elect from its membership a chairman and shall elect an executive director, who shall not be one of its members.

(b) The executive director shall be subject to the rules and regulations of the board of trustees and shall be the treasurer of the assets of the retirement system. All payments of the funds of the retirement system shall be made by the executive director and only upon vouchers signed by him and countersigned by one other person designated by the board of trustees. The executive director shall furnish the board of trustees with a surety bond issued by a company authorized to do business in this state and in such an amount as shall be required by the board of trustees. The premium on such bond shall be paid from the expense fund provided for in Code Section 47-3-47.