Bibliography: Der Heilige Wald von Bomarzo pub Berlin 1996 
Scultura del Cinquecento in Italia Meridionale by F. Negri Arnoldi Naples 1997 no.124 
Das Monster-Portal am Palazzo Zuccari in Roma. Wandlungen eines Motivs vom Mittelalter zum Manierismus, Zeitschrift für Kunstgeschichte 32. Bd. H.3/4 (1969) pp.229-261 (fig. 2) 
Shapes of Earth and Time in European Gardens, Art Journal No.42 No.3 Earthworks: Past and Present (Autumn 1982) pp.210-216 (fig4) 
La Scultura del Cinquecento by Giovanni Mariacher pub.1987 p.151.

Note: The mask compares with mannerist carvings by Andrea Calamech (c.1514-78) who played an important role in establishing a vogue for Tuscan mannerist influences in Sicily. A comparison can also be drawn with the enormous 'Hell Mouth' created for Vicino Orsini between 1550 and 1584 in the Bomarzo garden in the Parco dei Mostri in Florence; the wide open mouth flanked by two long deep creases and in particular the area around the bridge of the nose and in the stylised eyebrows. 

The Palazzo Zuccari in Rome built in the late 16th century for the painters Frederico and Taddeo Zucarri, also expresses this influence in the enormous face with furrowed brows whose wide open mouth surrounds the door.