Section 553. Additional pension benefit for members of optional twenty year retirement plan

a. A participating employer  which  has  elected,  or
  which  elects  to  provide  the  benefits  of  the  optional twenty year
  retirement plan for its employees as specified in section  five  hundred
  fifty-two  of  this  article  may  elect  to  make contributions for the
  purpose of providing an additional pension pursuant to this section  for
  members  in its employ who are entitled to a pension pursuant to section
  five hundred fifty-two of this article.  Every  member  employed  by  an
  employer  which  participates  in  the  retirement  system and which has
  elected the provisions of section five hundred fifty-two of this article
  and this section may elect to be  covered  by  the  provisions  of  this
  section  by filing with the comptroller a duly executed and acknowledged
  form prepared by the comptroller for that purpose.
    b. Upon retirement, each such member shall receive, for each  year  of
  service  in excess of twenty, an additional pension which shall be equal
  to one-sixtieth of his or her final average salary; provided, however, a
  participating employer may elect to provide any  service  credit  earned
  with  a  public  employer  prior  to  services  performed  as a sheriff,
  undersheriff or deputy sheriff towards the  one-sixtieth  allowance  and
  provided  further  that  the  total  allowance  payable pursuant to this
  section shall not exceed three-quarters of such member's  final  average
  salary.  The  additional  benefit  provided by this subdivision shall be
  available to a member after his or her  employer  elects  to  make  this
  benefit  available to all its members otherwise eligible to receive this
  benefit.