Chill shrimp several hours in dressing, turning them occasionally.
Meanwhile dissolve gelatin in hot water.
Chill till partially set.
Combine remaining ingredients; mix well.
Stir into gelatin mixture.
Turn into 5-cup ring mold.
Chill till set.
Unmold; fill center with drained shrimp, add ruffle of water cress.
Pass bowl of mayonnaise or salad dressing.