Upon certification by the bar library committee, any librarian of a law library existing under the provisions of section 11-19b may retire after thirty years of service, and shall thereafter receive an annual pension equal to two per cent of his average annual salary for each year of such service based on the five highest paid years of service, payable in monthly installments; provided any such librarian having less than thirty years’ service on October 1, 1960, shall not be granted such a pension but shall be eligible for membership in the state employees retirement system, subject to such terms and conditions as to service credit and contributions to the retirement fund as the State Employees’ Retirement Commission determines. This section shall not apply to any librarian who is a member of the municipal employees’ retirement system or who is receiving a pension under the provisions of any special act.