Elgin Grade 44, An Unusual Watch Case

Now and then I come across an uncommon case type.  For example, I've only seen 2 or 3 like this one.  The movement is held in a completely separate ring, which snaps into the rest of a case using a spring loaded latch.  Unlike a typical swing-out case, the movement, in the ring, installs from the back.  There is no bezel.  The front of the case is all one part.

This is an Elgin grade 44 pocketwatch movement, 18 size, 17 jewels, made about 1895.