There shall be a general election for county supervisors, county superintendents of education, sheriffs, coroners and clerks of the courts of common pleas held in each county at every alternate general election, reckoning from the year 1960, except in those counties in which the term of office of any such officers may be for a period other than four years. In such cases elections to fill such offices shall be held at the general election next preceding the expiration of any such term of office.