The retainer ring it threaded. The slots you see are so you can grab it with a pin wrench. Typically, these retainer rings are spikes or dimpled to keep them from vibrating loose.
Before hitting/ruining the retainer ring with a hammer and drift, drill out the dimples if they are there (1/8 in drill, maybe an 1/8 in deep) then back the ring out with a pin wrench. If you don't have a pin wrench, you can make one with a piece of flat steel and a couple small bolts.
Do a search on this site for ideas on how to remove the bearing retainer ring.