Pan Am Railways, Inc. (PAR), formerly known as Guilford Rail System (GRS) before March 2006, is an American holding company that owns and operates Class II regional railroads covering northern New England from Mattawamkeag, Maine, to Rotterdam Junction, New York. The primary subsidiaries of Pan Am Railways are Boston and Maine Corporation (reporting mark BM), Maine Central Railroad Company (reporting mark MEC), Portland Terminal Company (reporting mark PTM), and Springfield Terminal Railway Company (reporting mark ST); BM and MEC are operated under lease by ST.