This is a First Pattern Model 1855 Rifleman's Belt that was issued with the Model 1855 Rifle.  The permanently attached frog was for the Model 1855 Bayonet.  

The first pattern belt is identified by the asymmetrical straps connecting the bayonet frog to the belt.  The rear strap is much wider at the top than the front strap.

This belt and bayonet saw service during the US Civil War and is well documented in period photographs.

This information, including the pictures, has been provided by Kenneth L. McPheeters from his website McPheeters Antique Militaria.