This is a half plate dag of an unknown Naval officer.  It has a complete leather case which is split. The designs are different so I probably married one side, I can't remember.  Both clasps are present.  This image was found in Nashville Tennessee and I have been unable to identify the subject.  He is wearing an early naval uniform which was used until 1862 so I don't know if it is Mexican War or early Civil War.  What I can see of the belt buckle is from that same era.  The image is exceptionally clean.  There may be a couple of light scratches on the right sleeve.