Wide-angle lens for the Nikon S series — the W-Nikkor 35mm f2.5.
This particular item is astonishingly unopened!
Serial number: 266xxx.
While the seal remains unbroken, the serial number suggests that this is the later, lightweight version, featuring a black-painted aluminum barrel (presumably, of course!).
The lens construction is a 4-group, 6-element double Gauss design.

Factory-sealed and brand new.
It remains wrapped in the original plastic and is sealed with a NIPPON KOGAKU TOKYO paper sticker.
There is some peeling on the plastic wrapping.

Unopened Nikon items are exceptionally rare — this is simply a precious find.