A drawing of a Bacchic procession and sacrifice, among trees - possibly copied from an unidentified antique relief, or an invention in the antique style. 

The drawing had been classed among the school of Giulio Romano. Popham (note on mount) first thought it might be Girolamo da Carpi, the standard attribution for such drawings, but later catalogued it (in P&W) as by Pirro Ligorio, and the style of the faces supports this attribution. 

A similar subject is found in a drawing by Ligorio in the Ashmolean Museum in Oxford (Inv. 386), The Drunkenness of Silenus. In the Victoria and Albert Museum, previously attributed to Polidoro da Caravaggio, is a Sacrifice to Ceres (Inv. 266).