What does "s.d." mean here?

"32. Percy, Mahomet, ‘The Properties’.
33. Ibid., 1.1.26.
34. Ibid., 1.1.31, 49.
35. Ibid., 4.3.347.
36. Ibid., 4.6.37.
37. Ibid., 5.4.6.
38. Ibid., 5.13, s.d.
39. Ibid., 5.13. 3– 4.
40. Ibid., 5.13.129, s.d.
41. Ibid., 5.13. 9–14. "

The source: Jerry Brotton, This Orient Isle- Elizabethan England and the Islamic World, the footnotes of Chapter 11.