Brass number 115 Bohannan switch lock from the Eastern RR, which became part of the Boston & Maine in 1890.  I don't have the opener so cannot test it, but it is tightly locked and had play in the locking arm.  Has original iron chain attached.  The dustcover no longer is sprung.  ERR on locking arm.  All in all a nice lock in pretty good shape, and a great addition to a collection.  Please ask any questions before bidding.  Thanks for looking!!