Source : Webster's Revised Unabridged Dictionary (1913)

Credulously \Cred"u*lous*ly\, adv.
   With credulity.

Source : WordNet®

credulously
     adv : in a credulous manner; "the children followed the teacher
           credulously" [syn: {believingly}] [ant: {incredulously},
            {incredulously}]