22mm, Unidientified unit Coat Button marked "MRL" with early "Wadhams Webster & Co" rmdc backmark. This is a rare unlisted button with a wonderful early backmark that can be dated to 1838-46.  It very well could be associated with the Mexican-American War and there is some credible (but, inconclusive) thought that it may be assoiciated with Maine.  The "L" likely stands for "legion" or "lancers."  If you have or know of the attribution of this wonderful button, please share.