Since most of the fossils found in the Mahantango are internal molds or external casts, snails can easily be overlooked as they can be less recognizable. I have been lucky enough to get some obvious enough examples to be able to ID the genera of some of my finds.
Paleozygopleura - I wish I could find more of these but they apparently don't preserve well and I only find them as faint impressions. As you can see it's a high spired shell with fine ribbing along the length.
Bucanopsis - This mold has preserved some of the external ornamentation. You can see how the shell sweeps out at the front where the snail's body would have been.
I think this might be an internal mold of a Bucanopsis or some other snail from the Bellerophontidae family.
Crenistriella - I find this genera often but only rarely can I find the external ornamentation. The first picture below is a view up into a cast (with the mold in subsequent pictures) where you can see the fine lines that decorated the shell.
These next two I'm not sure of. The first could be Euomphalus and the second might be Bembexia. Both are fairly large but slightly distorted internal molds with no external casts.
Cyclonema - This snail is common from the Ordovician up into the Devonian and sometimes is found intimately associated with Crinoids where it would live on top of the anus of the Crinoid and consume the waste products.