yeah, they are called "littleneck" clams up here in the northeast, but that is a nickname I think, they might be called something else in other parts of the country. You will have to go to a grocery store that has a nice seafood section.
They should be closed. IF they completely open up, then they are dead.
They are pretty cheap. a dozen for $6....so 50 cents a piece.
I just throw mine in, and they have been fine.
....and if you enjoy eating seafood, be sure to get a few extra!