Folding Lap Desk

 

This period lap desk has several compartments and when folded can be locked.  Constructed of maple, felt, and brass, it measures about 6″ x 20″ x 20″.  For source and more details, click here.

 

Image from: http://www.cr.nps.gov/museum/exhibits/revwar/image_gal/morrimg/deskbox.html