The Atlantean codex is a trinket obtained in booty divisions from Atlantis. It was first seen in release 2009-12-08. The Atlantean codex is available in all the colors of the Atlantean trinket palette.
Note: A booch was made in the initial release allowing this trinket to potentially be found in all cloth colors save persimmon. This was fixed in release 2009-12-10 - all trinkets that had already been won remained unchanged irrespective of color, but all future trinkets could only be won in Atlantis-palette colors. All possible colors may be seen here.