My wind band is playing Saint-Saens' Pas Redouble, using the Josneau arrangement published by Evette & Schaeffer. It's on IMSLP. The bassoon part is mostly in bass clef, but occasionally uses a clef I've never seen before. I assume it's a variation of a C (tenor) clef. You can see it after the 8 bar rest below.
Stanford and Forsyth showed the historical evolution of the tenor clef in this image (found here).
Does anyone have a more authoritative source confirming that this is a tenor clef?
It would be conclusive if there were a key signature shown in that clef, but in this piece, the key signature is shown in bass clef only. Tenor clef would mean e-natural and f-sharp accidentals, which seems quite reasonable.