Source : Webster's Revised Unabridged Dictionary (1913)

Placidly \Plac"id*ly\, adv.
   In a placid manner.

Source : WordNet®

placidly
     adv 1: in a quiet and tranquil manner; "the sea now shimmered
            placidly before our eyes"
     2: in a placid and good-natured manner; "I put the questions,
        and she answered them placidly"