We call 'em "rocking chair" seats. Chrysler did away with them in 89 or 90. The manual seats, in addition to sliding forward and back on the standard flat rail, have a second, arched rail (curved up at the ends, down at center) that allows the entire seat to "rock" -- it changes the angle of the seat and the backrest together, so if you like a lot of thigh support you rock it back, and if that cuts of the blood supply to your legs you rock it forward.
It's a nice feature, but in all honesty I set the driver's seat in my '88 where I liked it within the first week I had the vehicle, and I don't think it has been moved since. My wife sometimes rocks the passenger seat, but she always ends up setting it back to the neutral position so I don't know why she bothers.