Cell type: Selenium
Measure type: Reflecting/averaging
Gossen is a German company that, along with Sekonic, made about 10,000 different meters and gave them similar names. Gossen loves the words "Six" and "Luna," so there are all kinds of varieties of "Luna" meters and "Six" meters, and yes, there's a LunaSix in there somewhere (it's called the Luna Pro in America).
This is nothing special except for one really neat thing: there's an integrated case-cover that protects the meter when not in use. When you're ready for it, you hold the cover, pull the meter down, and then flip the cover back over. The pictures here aren't great but you get the idea.
The only bad thing about this is that the cover is bakelite, just like the rest of the meter case. Bakelite is super hard and shiny and it looks great and it takes a lot of light abuse very well, but if you drop it, it will chip or crack fairly easily. That's the nice thing about metal: if you drop it, it tends to ding or dent, and leather gets scuffed or scarred, but it offers some protection.
There are several versions of this, from what I've seen on the net. It was built between 1937 and 1955. Film speed here is calibrated in DIN and Scheiner, so I believe it was built for Europe, not the American market. I have no idea where it falls by date. Gossen made Sixtus meters for nearly twenty years—it could be anywhere in there, and they didn't start advertising in US magazines (that I'm aware) until the 1960s.