Cortez snails range in size from an inch to 1.75''. These snails will consume diatoms, detritus, cyano and algae in the substrate as well as on rocks, and glass in your aquarium.
They take time to "come out of their shells" and move about after placing them in your tank. Please give them at least 72 hours to start moving about. It is abnormal for them to move around right away. Additionally, when the snail is pulled into its shell, the opperculum can pull back around the corner of the circular opening. The shells are not empty, that is just how this species is.