Section 21. If the land mentioned in section fifteen lies entirely in one town, the petition may be made to the mayor and aldermen or selectmen thereof, who shall proceed thereon in all respects as above provided for county commissioners, except that they need not give notice to their town. Such petition shall be filed in the office of the town clerk before proceedings are had thereon; and the petition with the order thereon shall be recorded in said office within two months after the order has been made.