These appear to be a littorinid species. The label below the tray said they were "mud snai".
The members of the family Littorinidae are intertidal, semi-terrestrial snails whose ancestors stopped short of evolving to be fully terrestrial. They were the subjects of two old posts here and here.
In the next tray were these larger snails labeled "shell conch". My ignorance of the taxonomy of most marine gastropods prevents me from attaching even a family name to them.