A tournure or bustle pad was the right thing…

.. to wear with the new form, as the small bustle which had been used for a few years prior, were not needed with the cuirasse or Princess sheath dresses, but a small pad or “tournure” helped lift the trims, draping, bows, and frills in the back over the rear end so that they would drape more elegantly.

(Photo: reproduction tournure from the 1879 era)