The 'Zwitter' was a transition model Beetle that retained the 'split rear window' but introduced many of the new 'Oval window' parts such as the updated dashboard, so the easiest way to spot one is to look at the rear window and the dash - if it's a split rear window but an oval style dash then it's a 'Zwitter'.
This was a major update to the look of the split window era Beetle, whilst retaining the 25hp engine and running gear. Chrome trim was added to the split rear window (unless it was a 'Standard'), the side trim lost it's groove and became smooth, as did the bumpers. Simpler and smoother 'popes nose' licence plate light was added along with new slightly bigger twin lens tail lights. Inside remained largely the same as the split except for the new dashboard, with the batwing steering wheel retained, grooved interior door handles and ribbed doors. Gone are the crotch coolers from the front quarters, replaced by quarter light windows in the doors.
The old 16" wheels were replaced with 15" versions, although visually they were identical apart from the size. The Beetle still had no turn signals other than the semaphores mounted in the 'B' pillar, which were still the ribbed cover style.