I don't know what it is

I bought this bike brand new from Joe at the bike shop in Cocoa Beach, Florida, in September of 1991. I used most of my second paycheck from my first "career" job after college; it came to around $550. Over the next 20 years, I put about a zillion miles on it, many of them on the beach in Cocoa Beach/Cape Canaveral, but I did take it to Europe with me in 1992. It pretty much went everywhere I went.
I've replaced the derailleur and chain/cables, normal stuff, and added the bars to the...