Wide-angle lens for the Nikon S series — the W-Nikkor 35mm f2.5.
Amazingly, this one is still unopened!

It features a Tessar-type optical design with 4 elements in 3 groups.
Serial number 4389xx.
This serial range falls within the transition period from the early chrome version to the later black version, so it's unclear which variant this is.
Manufactured around 1956 — the era of the Nikon S2.

Chrome or black...
We’re dying to open it and find out — but that would be the forbidden move.

Factory-sealed and brand new.
It is still wrapped in its original plastic and sealed with a NIPPON KOGAKU TOKYO paper label.
There is some peeling on the plastic in a few areas.

An unopened Nikon item like this is extremely rare — simply invaluable.