OT: Strange tempo indication

[Urs Liska]

I'm wondering about the "T." in a 18th century print. The file is too large to attach here, so please view at https://git.openlilylib.org/bfsc/kayser/issues/3.

First I thought it referred to the tenors, but it's obviously not related to that. It's in all the parts, and I've also seen it with other tempi. What's confusing me is also that it's not in italics while Gravè is.

Any suggestions?

Urs