Stuck in gear

Took the Dart for a drive yesterday. The trans (4 spd) stuck in 3rd. I turned around & was heading home & was able to get it to start shifting again. Turned back around and went to a car show. The Dart shifted fine the rest of the way to the show and almost all the way home. Stopped at a light in town (didn't downshift). When I went to put the trans in 1st the trans was stuck in 4th. The shifter would move but it wouldn't go into any other gear. Put the shifter in 4th, got going & the thing started shifting just fine again.

Any ideas?