The Frame Plate / Cover Plate of the Otis Series 5 "Egg Lantern". According to Unitec, they call it the Slim Series 5 Lantern.
Brochure:
www.unitecparts.com/wp-content/uploads/2013/01/07-HallLanterns-W.pdfarts.com/wp-content/uploads/2013/01/07-HallLanterns-W.pdf)
*Pages 26 & 33*