Columbia subject headings:
Paleobotany--Canada.
Paleobotany--Devonian.
Paleobotany--Silurian.
Harvard subject headings:
Paleobotany--Canada.
Paleobotany--Devonian
Paleobotany--Silurian
Princeton subject headings:
Paleobotany--Canada.
Paleobotany--Devonian.
Paleobotany--Silurian.