(b) Any member in service whose duties require the board to classify him in two groups as set forth in paragraph (2)(g) of section three and whose regular compensation is paid from two appropriations shall, on attaining the maximum age for retirement of employees in the group having the lower maximum age limit, cease to perform any duties of a member in such group. If the major portion of his regular compensation is in payment for such duties he shall be retired forthwith from service. If the major portion of his regular compensation is in payment for duties in the group having the higher maximum age limit he may continue to perform such latter duties until such maximum age, in which event no portion of his allowance shall become effective until the date of his actual retirement following the cessation of all duties.

[There are no paragraphs (c) to (f).]