(a) Ports-of-Entry for aliens arriving by vessel or by land transportation. Subject to the limitations prescribed in this paragraph, the following places are hereby designated as Ports-of-Entry for aliens arriving by any means of travel other than aircraft. The designation of such a Port-of-Entry may be withdrawn whenever, in the judgment of the Commissioner, such action is warranted. The ports are listed according to location by districts and are designated either Class A, B, or C. Class A means that the port is a designated Port-of-Entry for all aliens. Class B means that the port is a designated Port-of-Entry for aliens who at the time of applying for admission are exempt from document requirements by §212.1(c)(5) of this chapter or who are lawfully in possession of valid Permanent Resident Cards, and nonimmigrant aliens who are citizens of Canada or Bermuda or nationals of Mexico and who at the time of applying for admission are lawfully in possession of all valid documents required for admission as set forth in §§212.1(a) and (c) and 235.1(d) and (e) of this chapter and are admissible without further arrival documentation or immigration processing. Class C means that the port is a designated Port-of-Entry only for aliens who are arriving in the United States as crewmen as that term is defined in section 101(a)(10) of the Act with respect to vessels.