No other provision of law in any other statute which provides wholly or partly at the expense of the State of Alabama or of any political subdivision thereof for pensions or retirement benefits for teachers of the said state, except as may be provided by state and federal laws for coverage under the provisions of the Federal Old Age and Survivors Insurance System of the Social Security Act, shall apply to members of the retirement system established by this chapter; provided, that if any member who filed an enrollment with the Board of Control on or before September 1, 1942, and who was certified to the Board of Control as an employee of a county board of education which had a statutory pension plan in effect on September 1, 1941, should receive upon retirement on or before July 1, 1950, a retirement allowance less than the pension which would have been provided for him under the local pension plan, then such member shall be eligible to receive a supplement to his retirement allowance payable from funds provided by said county board of education in an amount sufficient to make his total retirement allowance equal the amount which he would have received if he had been retired under the provisions of the local statute.