Hi Max,
It's probably 19th century, and the lid is most likely pewter. Lidded tankards were common back in those days.
I think it's possible that some damage has occurred to the lid and part of the handle.
First of all, the bit on the handle that is sticking up, like a thumb-grip, may be just that. Or it may really have started out being flat against the handle, doing a job of support. The fact that the handle is "wobbly" suggests that some internal substance, between the pewter and the glass has, over the years, simply degraded and fallen out.
Or as you suggest, it could be a (poorly repaired) lid applied to a basic tankard that started out without a lid!
I think the lid is definitely missing a finial to the rear, above the point of connection to the handle. The finial would have allowed easy lifting of the lid, with retention of same during drinking by hooking the thumb over the finial when the lid was in the raised position.
Clear glass tops to pewter lids are often seen.
Here's a pic of one I have, which I reckon is 19th century German as the lid has a nice embossed image of perhaps the first steam train at Nurnburg (not seen in the photo):
http://tinypic.com/9708za.jpg