Please clarify for local discussion.
Referencing the attached sketch:
First is a coin simulating a fossil. If split at the red line, there would be 2 pieces of external mold. Correct ? or incorrect ?
Second is a lens shape, like a saucer or moult of a pygidium. If split at the red line, there would be 2 pieces of external mold. Correct ? or incorrect ?
Third is an egg or complete bivalve. If split at the red line, there would be 2 pieces of external mold and 1 internal mold. Correct ? or incorrect ?
All 3 assume that the specimens have dissolved an left a void which if filled would be the cast. Correct ? or incorrect ?
The local argument is that the pygidium moult example is 1 external mold (top) and 1 internal mold (bottom) because it is the "internal" side of the animal. I don't think that is correct.
Just a local discussion needing clarification, thanks.
ref:
http://www.ucmp.berkeley.edu/paleo/fossilsarchive/casmol.html