A certain kind of book

I'm casting my mind about and trying to remember something, maybe from 4th ed.

Was there ever a type of book where you needed to know the spell the book was about?
I can remember the three types from 4th ed, Summae, Tractatus and Libri Quaestionum (spelling?) but can't remember if this spell-based-book is something that was or something I've just made up.

Just took a glance at my 4th ed book, and all three types could be about Arts or Knowledge, but not about spells.

In 5e, you can have a Tractatus about a Spell Mastery, which would only be useful if you know the spell in question. Is that the one you're looking for?

You're thinking of Tractatii, where you had to master a given spell before you could write a tractatus about it.

Your spelling for all three is flawless. You get bonus points for getting right the plural of Tractatus, which is indeed Tractatus and not Tractati or Tractatii (a common mistake)!

Additionally, the reader of a tractatus "must already know the spell which the tractatus concerns, but need not have mastered it." You can't learn the spell from the tractatus. (pg 190)

Cool, thanks guys, nice to know I'm not remembering stuff that never happened.

No, that's Criamon 201.