The Secret Commonwealth of Elves, Fauns, and Fairies, by Robert Kirk.

The attribution of this to Scott rests on a letter by George Ticknor, in Allibone’s Dictionary (vol.  II, p. 1967) in which he says:  “Kirk’s Secret Commonwealth, a curious tract, of about a hundred quarto pages, on Fairy Superstitions and second sight, originally published in 1691, and of which, in 1815, Mr. Scott had caused a hundred copies to be privately printed by the Ballantynes, with additions, a circumstance, I think, not noted by Lockhart.”  Mr. Lang thinks the book was never printed until 1815.  (See his edition, London, 1893).  This 1815 edition of 100 copies was made, he says, from a manuscript copy preserved in the Advocates’ Library, for Longman & Co.  He quotes one of Scott’s references to the book, but does not intimate that Scott was the editor.

  Memorie of the Somervilles; being a history of the baronial house of
  Somerville, by James, eleventh Lord Somerville. 2 vols.  Edinburgh.
  [Edited by Scott anonymously.]

      The additions by the editor consist of a short preface and
      abundant notes.

1816
  Paul’s Letters to his Kinsfolk.  Edinburgh.

      These letters were anonymous, but Scott was always recognized as
      the author of them.  They are contained in the Miscellaneous Prose
      Works.

  The Antiquary.

  Tales of my Landlord.  First series: 
    The Black Dwarf. 
    Old Mortality.

1817
  Harold the Dauntless.

  Rob Roy.

1818
  Tales of my Landlord.  Second series: 
    The Heart of Midlothian.

Burt’s Letters from the North of Scotland ... the fifth edition, with a large appendix, containing various important historical documents, hitherto unpublished; with an introduction and notes, by the editor, R. Jamieson ... and the history of Donald the Hammerer, from an authentic account of the family of Invernahyle (by Scott:  see a note accompanying the text). 2 vols.  London.

Scott’s contribution is short.  See also Appendix IV, which is taken “from a manuscript in the possession of the Gartmore Family, communicated by Walter Scott Esq.”  Scott’s name had become so valuable that the publishers tried to put it on the title-page of this book, to his great indignation. (See Constable, III, III, 119-20.)

1818-24
  The Encyclopaedia Britannica:  Supplement. [For this work Scott wrote
  the following essays:] Chivalry, published in 1818; The Drama,
  published in 1819; Romance, published in 1824. (These are given in the
  Miscellaneous Prose Works.)

1819
  Tales of my Landlord.  Third series: 
    The Bride of Lammermoor. 
    A Legend of Montrose.

  The Visionary, by Somnambulus. (A political satire in three letters,
  republished from the Edinburgh Weekly Journal.) Edinburgh.