A present employee who was a contributor to a municipal pension fund which has been merged into and become part of the fund in accordance with The 1921 Act or this Article who withdraws after such merger having 20 or more years of service and for whom the amount of annuity provided by this Article is less than the amount stated in this section has a right to receive annuity as follows:
In addition to the combined age and service and prior service annuities to which an employee is entitled (except one in receipt of pension or annuity from the annuity and benefit fund herein provided for on June 30, 1935), an employee with 35 or more years of service who has attained age 65 or more at the time he withdraws, is entitled to receive a sum equal to the difference between the combined age and service annuity and prior service annuity, and 50% of his highest "actual compensation", but not in excess of 33 1/3% of the combined age and service annuity and prior service annuity.
40 ILCS 5/8-136