Pick oysters free of any shells. In a deep buttered casserole, mix together crackers, bread crumbs, and melted butter. Place a thin layer of crumb mixture in the bottom of the casserole. Cover it with half of the oysters. Season cream with nutmeg, salt, pepper and celery salt (if using). Pour half of this mixture over the oysters. On the next layer, use the oysters, 3/4 of the remaining crumb mixture and cover that with seasoned cream. Top with the remaining crumbs. Bake for 20 to 25 minutes, or until lightly browned.