An employee who was a contributor to and participant on December 31, 1965 in a Public Library Employes' Pension Fund which has been merged into and becomes part of the fund provided for in this Article, and who withdraws after such merger, shall have an optional right, in lieu of any other annuity, to receive annuity as follows:
(a) $60.00 A month after the date of withdrawal if he then has 20 or more years of service and is age 50 or more years, plus an additional $7.00 a month for each additional full year of service after 20 years, with such total monthly annuity not to exceed 60% of the maximum monthly salary received during the employee's term of service, or the sum of $200.00, whichever is the lesser.(b) $30.00 A month after the date of withdrawal if he has 10 or more but less than 20 years of service and is then age 55 or more years, plus an additional $3.00 a month for each additional full year of service after 10 years.