M. Rao and H. Singh, “Palynology of the Barail (Oligocene) and Surma (Lower Miocene) sediments exposed along Sonapur-Badarpur Road Section, Jaintia Hills (Meghalaya) and Cachar (Assam). Part - III. Pteridophytic spores”, JPS, vol. 35, no. 1-3, pp. 267–280, Dec. 1986.