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, or the President of Council, or of three (3) members of Council. Any such request shall state the time, place and date thereof and the subject or subjects to be considered at the meeting. Unless four (4) members in attendance concur, no other subject or subjects shall be considered. Notice in writing of each such special meeting called at the request of the Mayor, President of Council, or three (3) members of Council shall be given to each member of the Council and the Mayor by serving the same on each of them personally or by leaving a copy thereof at their 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 or subsequent to such meeting, and shall be deemed conclusively to have been waived by any member of Council or the Mayor who is present at such special meeting.