The legislative body may approve, modify or disapprove the recommendation of the planning commission; provided that any modification of the proposed ordinance or amendment by the legislative body not previously considered by the planning commission during its hearing, shall first be referred to the planning commission for report and recommendation, but the planning commission shall not be required to hold a public hearing thereon. Failure of the planning commission to report within forty (40) days after the reference, or such longer period as may be designated by the legislative body, shall be deemed to be approval of the proposed modification.