Scrub clams well with a brush under cold water; place in a wide heatproof serving bowl at least 1 inch deep.
Sprinkle garlic, parsley, and lemon juice over clams; dot with butter.
Place bowl on rack in wok over 1 1/2 to 2 inches boiling water.
Cover wok and steam for 10 minutes or until clam shells open (discard any unopened clams).
Lift bowl from wok, dry base with a towel, and serve.
If you wish to serve rice, spoon it into 2 bowls.
Arrange clams in each bowl on top of rice, and ladle broth over all.