What does „Turr.“ in an apparatus criticus refer to?

In Burnet's edition of Plato's "Philebus," at 34b6, there is a reference to "Turr." I am unable to figure out whether that refers to a MSS or an Editor. I have exhausted my Google Scholar, Google Books, Google Search skills. The only possible match I could come up with is "Johannes de Turrecremata". But I was unable to check this. I would be extremely grateful for any advicr or help!