It's a twist to open single edge razor. Was made from the mid-30's into the 50's.
Most common style is open comb, which is also considered to be the most agressive. At the same time, a model called the Clog-Pruf was made with a serrated safety bar and large cutouts for lather and whisker flow. In the 50's they were sold with more conventional safety bars.
White metal and gold were available finishes, there were two different styles of TTO knob shape, plus an ivory colored plastic knob for the later style.
This is a very plentiful razor. You should be able to pick it up on B/S/T for less than $12.
Just about any mixed lot of old razors on eBay should include a Micromatic.