Source : Webster's Revised Unabridged Dictionary (1913)

Incredulously \In*cred"u*lous*ly\, adv.
   In an incredulous manner; with incredulity.

Source : WordNet®

incredulously
     adv : in an incredulous manner; "the woman looked up at her
           incredulously" [syn: {unbelievingly}, {disbelievingly}]
           [ant: {credulously}, {credulously}]