Columbia subject headings:
Paleontology--Ordovician.
Paleontology--Scandinavia.
Trilobites--Scandinavia.
Harvard subject headings:
Paleontology--Ordovician
Paleontology--Scandinavia.
Trilobites--Scandinavia.
Princeton subject headings:
Paleontology--Ordovician.
Paleontology--Scandinavia.
Trilobites--Scandinavia.