Place the clams into a large pot together with the salt and half cup of water. Place over high heat and steam the clams for about 5 minutes, shaking the pot frequently, just until the clams open. Drain the clams. Remove clams from the shells, discarding any shells that have not opened. Mince the clams. Rinse and dry 18 half shells. In a mixing bowl, combine clams and all the remaining ingredients. Mix well, and toss the mixture lightly against the inside of the bowl to combine and compact it. With a spoon dipped in cold water, stuff the reserved shells with this mixture, mounding it and smoothing it. Arrange clams on a tray in a steamer for 20 minutes.