Snails: Order Grastropoda
Shells of terrestrial snails (Gastropoda: Pulmonata and Prosobranchia) are rare in amber. Shells of terrestrial snails in Mexican amber have been identified as Spiraxis sp. (Spiraxidae), a member of the Ferussaciidae. Shells are some of the rarest fossils in amber. They are normally very small and very rare.
This particular piece of amber reminds me of a brick. It is about 2 inches long by .75 x .75 inches. Quite an attractive piece of amber.
Here is a scanned image of the snail next to a ruler so you can see the actual size.