All expenses of the Public Employees Retirement Board in excess of those paid under ORS § 237.490 (2) incurred in administering the provisions of ORS § 237.410 to 237.510, including such proportion of the salary of the director, counsel, professional consultants and employees of the retirement board, as the time required of them for the administration of ORS § 237.410 to 237.510 shall bear to the time required for the administration of both ORS § 237.410 to 237.510 and the public employees retirement law, shall be paid in the manner provided by law, out of the Social Security Revolving Account. For such purpose, the board may make monthly withdrawals from said account in lump sums. The board may, under such rules as it promulgates, collect from each public agency its respective pro rata share of the expenses incurred in administering ORS § 237.410 to 237.510. Each public agency included in the agreement pursuant to ORS § 237.430 is required to pay its pro rata share of the expenses incurred by the board in administering ORS § 237.410 to 237.510. In order to facilitate financing the administration of the system the board may designate fiscal periods and may provide that extraordinary expenses incurred during one such period, such as expenses for equipment, may, for purposes of equitably distributing part of the burden of the expenses, be apportioned to subsequent fiscal periods in such manner as to the board seems equitable. [Amended by 1953 c.192 § 5(2); 1967 c.399 § 3; 1973 c.704 § 15]