Section 19G. A clerk of a city or town who also serves as a member of its board of registrars of voters shall, in addition to any compensation to which he may be entitled as city or town clerk, receive the sum of fifty dollars, and, if the number of registered voters exceeds one thousand, an additional fifty dollars for each additional thousand of registered voters or major fraction thereof, provided, however, that the total payment for such service as a member of said board shall not exceed fifteen hundred dollars in any year, except as provided in section nineteen H.