The slightly yataghan blade has wide unstopped fullers.

The scabbard shown is probably not original to this example.  It looks like a scabbard for the Model 1861 Whitney Navy rifle bayonet.  

There is very little known about this bayonet.  Only two pictures exist for the shown example and there are currently no available dimensions.  The style of the hilt is very similar to other known US brass hilted bayonets with some minor differences.  So labeling this bayonet as US is a guess at best.  The crudeness of the casting and minor differences in form makes calling it Confederate convenient until more information is recorded.