Here are a couple of pictures of comparable fossil forms:

http://www.clas.ufl.edu/users/pciesiel/gly3603c/fossils.html

http://www.themissinglink.biz/images/Ebay64.jpg

The first picture shows pieces of broken mouth plates.

The second picture shows mostly pieces of stingray tail spines, but also
includes a few mouth plate segments, at top center, and the left edge center
and left edge lower.

Sorry this is not really mollusk-related, but it does address the question
that was presented.

Paul M.