E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Dumachus.
The impenitent thief, called Dysmus in the apocryphal Gospel of Nicodemus. In Longfellows Golden Legend Dumachus and Titus were two of a band of robbers who attacked Joseph in his flight into Egypt. Titus said, Let these good people go in peace, but Dumachus replied, First let them pay for their release. Upon this Titus gave his fellow-robber forty groats, and the infant Jesus said