Windsor Chair Perplexing Me for 2 Years Now

Hi Everyone,
Picked this up for a song at a 2nd hand shop. It's been driving me nuts for over 2 years. It's painted, has 7 spindles, is low-backed and has no arms. It has a very prominent saddle seat. I can't find a single one like it no matter how hard I look. Any ideas?

In Kovel's 2013 edition, they describe a fanback chair and a comb back chair that have 7 spindles. Is this a fanback or a comb back?

Also, on the unpainted bottom of the seat there is a stamped in black ink number "55" with a mark that is hard to discern. Looks like a crown withi three little parts that stick up....um....sort of like the Trifari mark on jewlery.

Thanks in advance,
Michele