31681.53. (a) Except as provided in subdivision (b), a retirement allowance or optional death allowance, including an allowance payable to a survivor of a member, payable to or on account of any member of this system or of a superseded system who has been or was retired for service which did not on July 1, 1976 exceed five hundred dollars ($500) per month is hereby increased as follows: Number of years ofPercentage of increase in county or districtmonthly retirement serviceallowance25 or more years ........................ 10%20–25 years ........................ 8%15–20 years ........................ 6%(b) No allowance shall be increased to more than five hundred dollars ($500) per month pursuant to subdivision (a).This section shall not be operative in any county until such time as the board of supervisors shall, by resolution adopted by majority vote, make the provisions of this section applicable in such county.(Added by Stats. 1976, Ch. 627.)