The below case was my one prize from an otherwise fairly mediocre regional this past weekend. These cases are not hard to find, but this one was priced right and is my first example of the type.
Ezra Fitch, a Waltham employee, patented this design case in 1879. I believe it was the first use of a screw down crown in any watch, as well as the first implementation of the "modern" swing ring design used on many American pocket watch cases.
From the outside, this looks like a fairly typical American watch case of the era-it is a sterling silver "turnip" shaped case with a thick beveled crystal.
A few seconds playing with the crown, however, reveals a difference. The crown is secured down via a left hand thread. What this means is that crown is turned in the winding direction to unscrew it, and turned in the ratchet direction to screw it back down. This also means that if the watch is fully wound, the crown can not be unscrewed without engaging the setting mechanism.
Here it is with the crown unscrewed.
The bezel simply unscrews(in the fashion of a typical later swing ring case), revealing both the swing ring and the setting lever.
With the crown unscrewed, it is possible to lift the movement out. The movement in this watch is a fairly unexciting PS Bartlett grade 1877 model.