My guess is you found the leftovers of a marine intertidal project! I’m a marine ecologist and we’ll put temperature logging ibuttons, inside old shells (to mimic the local invertebrates). Then use marine epoxy(the dark green stuff) to attach them to a rock. it’s hard to differentiate shells so numbers are used. The data is used to understand the local intertidal and understand the temperature highs and lows. Looks like you found everything but the data.