Columbia subject headings:
Harvard subject headings:
Natural history--Canada, Western--Periodicals.
Natural history--Mexico--Periodicals.
Natural history--Periodicals
Natural history--West (U.S.)--Periodicals.
Princeton subject headings:
Natural history--Mexico--Periodicals.
Natural history--Periodicals.
Natural history--West (Canada)--Periodicals.
Natural history--West (U.S.)--Periodicals.
Periodicals.