The Secretary of the Commonwealth shall, not later than the thirtieth (30th) day next preceding the day fixed for any special election to fill a vacancy in the offices of United States Senator, Representative in Congress, Senator and Representative in the General Assembly, certify to the proper county board or boards the names and residences of, and parties or political bodies represented by, all candidates whose nomination certificates or papers have been filed with him, as herein provided, for such election, and have not been found and declared invalid, and to be voted for in the county or any district or districts thereof, substantially in the form of the ballots to be used therein.