Snails Again

-- [ From: Gene Bauman * EMC.Ver #2.5.02 ] --

Not to beat the snail subject to death, I have a quick question and then
will shut up.

I just got some mail-order pond snails "Black Japanese Trapdoor Snails -
Viviparis malleatus" and one has two small almost circular holes in the
shell. What is this a symptom of?  The treatment/cure?