This pistol is the second highest serial that have found a record for these little pistols. There are at present three variations of these pistols known, based on slide legends and method of assembly. Check this site, http://unblinkingeye.com/Guns/index.html, for further information on the Zehna and other interesting pistols.
The one presented here is, perhaps, the last designed method of assembly and until the acquistion of this one I had never encountered an example of such. Only a write up in A.B. Zhuk's "The Illustrated Encyclopedia of Handguns", illustrations 1774, 1775, 1776.