This is the scarce larger size of this great American button, and is from the William Guthman collection (He was a preeminent collector of Early Militaria and before his death was the Early American appraiser for the Road Show…Google his name…I bought this button at the auction and dispersal of his collection). Retains its original shank and is much more eye appealing in person than the magnified image suggests.
Images and description courtesy of William Leigh from CivilWarButtons.com at: http://civilwarbuttons.com/infantry