Hi Everyone!
It's an inkwell that was inserted in a desk at school. The moveable top piece was slid aside to enable the insertion of the inkpen nib. I used one of these when I was in 3rd grade and we were learning cursive.
I also had very long braids at the time. The little boy behind me unscrewed the top and inserted my braid end into the inkwell. Momma had a fit cause it messed up a brand new dress I was wearing that day. LOLOL