Cita APA (7a ed.)

Ludvigsen, R. (1979). A trilobite zonation of middle ordovician rocks, southwestern district of Mackenzie. Geological Survey of Canadá.

Cita Chicago Style (17a ed.)

Ludvigsen, Rolf. A Trilobite Zonation of Middle Ordovician Rocks, Southwestern District of Mackenzie. Ottawa: Geological Survey of Canadá, 1979.

Cita MLA (8a ed.)

Ludvigsen, Rolf. A Trilobite Zonation of Middle Ordovician Rocks, Southwestern District of Mackenzie. Geological Survey of Canadá, 1979.