APA (7th ed.) Citation
Society for the Study of Mediaeval Languages and Literature (Oxford, England), Onions, C. T., & Bennett, J. A. W. Medium aevum. Society for the Study of Mediæval Languages and Literature.
Chicago Style (17th ed.) Citation
Society for the Study of Mediaeval Languages and Literature (Oxford, England), C. T. Onions, and J. A. W. Bennett. Medium Aevum. [Oxford?]: Society for the Study of Mediæval Languages and Literature.
MLA (9th ed.) Citation
Society for the Study of Mediaeval Languages and Literature (Oxford, England), et al. Medium Aevum. Society for the Study of Mediæval Languages and Literature.
Warning: These citations may not always be 100% accurate.