Correct footnote:

Your footnote above should look like this:

*Four English Political Tracts of the Later Middle Ages*, ed. by Jean-Philippe Genet, Camden Fourth Series, 18 (London: Offices of the Royal Historical Society, 1977).

In your own work, the same footnote would look like this:

Four English Political Tracts of the Later Middle Ages, ed. by Jean-Philippe Genet, Camden Fourth Series, 18 (London: Offices of the Royal Historical Society, 1977).

Comment:

Note that the series title is not italicised or placed in quotation marks. The volume number is also not preceded by 'vol.'.

You will sometimes see the word 'Series' abbreviated to 'Ser.' and may encounter references in the form 'Camden 4th ser.'.

If you are citing an entire book, you do not need to include any page references. If you were citing an entire journal article, chapter, or short piece in an edited collection, you would just give the page span of the work.

In a bibliography, this work could appear alphabetised with the 'F's' as:

Four English Political Tracts of the Later Middle Ages, ed. by Jean-Philippe Genet, Camden Fourth Series, 18 (London: Offices of the Royal Historical Society, 1977)

or alphabetised under the 'G's' as:

Genet, Jean-Philippe, ed., Four English Political Tracts of the Later Middle Ages, Camden Fourth Series, 18 (London: Offices of the Royal Historical Society, 1977)

Whichever method you choose for your bibliography should be employed consistently.