In article ,
Chris Hogg wrote:

Neither my books nor a Web search helps. We have a Peziza (almost
certainly) growing in our drive, probably on conifers, with a
shining white interior and a buff exterior. Also, it cracks open,
irregularly, and is 1.5"-2.5" across.

Any ideas? I doubt that a photograph would help, not least as it
is very hard to get a good one.

I presume you've seen this, but without getting an answer.
http://www.fieldmycology.net/GBCHKLST/key.asp?KeyID=8

Yes. Like almost all semi-professional mycological texts, you
have to START by using a microsocope. While I have one, I have
never taught myself how to use it. Actually, that page is even
worse, and the very first key is:

Spores smooth or finely longitudinally striate under light
microscope; guttules usually absent, rarely present
Spores ornamented with fine (oil immersion!) to coarse warts or
reticulum under light microscope; guttules usually present, rarely
absent


Regards,
Nick Maclaren.