Special meetings of the Council may be called in accordance with and as provided for by its rules. In the absence of such provisions, special meetings may be called by motion of the Council taken at any regular or special meeting thereof; or shall be called by the Clerk upon the written request of the Mayor-President of Council, or of any three (3) members of the Council. Any such request shall state the time, place, and date thereof, and the subject or subjects to be discussed at the meeting; and no other subject or subjects shall be considered at such meeting unless four (4) members of the Council in attendance thereat so concur. Notice in writing of each such special meeting called at the request of the Mayor-President of Council, or any three (3) members of the Council shall be given to each member of the Council and the Mayor-President of Council by serving the same on each of them personally or by leaving a copy thereof at his usual place of residence not less than twenty-four (24) hours preceding the date and hour of such meeting. Service of such notice may be waived in writing, either prior to or subsequent to such meeting; and shall be deemed conclusively to have been waived by any member of Council or the Mayor-President thereof who is present at such special meetings.