Mix the shrimp, mayonnaise, soured cream, dill, onion and lemon juice together in a bowl and season with salt and pepper.
Toast the rye bread slices until crispy. Spread a layer of butter on each slice of rye bread.
Spoon a generous amount of the shrimp mixture onto each slice of bread. Garnish each serving with a dill sprig, if desired. Serve immediately.
