This bayonet has a typical Collins long hilt.  The smooth ribbed brass hilt is 125 mm long and has 14 ribs.  The muzzle ring is flush to the hilt flat and the inside diameter is 22.7 mm.  There is a forward swept round finial on the bottom of the guard and no finial on top of the muzzle ring.  The press stud and spring are typical Collins construction.  There is no steel rivet in the center of the guard.  The outer right side of the muzzle ring has been lightly flattened.  

The lug slot is chamfered on both sides around the top edge and there is no guide bar slot.   

On the only known examples, there are large font alphanumeric rifle mating codes stamped on the top of the muzzle ring.      

Only a few examples of this bayonet have been recorded and its origin and purpose remains a mystery.  So the following information is purely speculation based on what little information we currently have.

Based on the style of the hilt construction it most probably was made by Collins & Company.  The overall style and muzzle ring size leads one to believe it was made in 1860 to 1863 for the US Civil War.  

The flattening of the outside right edge of the muzzle ring is unusual for this period in US history.  Possibly done to allow a clear view of the rifle's site while looking down the barrel while the bayonet was attached.  Could this be an adaptation for a rifle that the bayonet was not originally designed for?  

The only known markings are rather large font alphanumeric rifle mating codes stamped on top of the muzzle ring.

Using the muzzle ring diameter, the lock-to-muzzle length and the unusually large dimensions of the lug slot, only the following four bayonets were found to be near identical.  Three unknown bayonets made by Collins & Company and the PS Justice Type 2 Bayonet.      

Unknown Collins Bayonet # 5, Reference # 125, appears to be nearly identical except for the unusual muzzle ring notch and guide bar slot.  Could Reference #125 be a musicians version of this bayonet?

Unknown Collins Bayonet # 8, Reference # 237, is also very similar to this bayonet. Except for the blade length and different style of markings.  Unfortunately, the lock-to-muzzle measurement is unknown and it is being estimated based on the images supplied.

Unknown Collins Bayonet # 7, Reference # 236, is also very similar to this bayonet. The flattening of the right side of the muzzle ring and the alpha numeric numbering are also very similar. The only serious difference is the short guide slot.  Unfortunately, the lock-to-muzzle measurement and the actual lug dimensions are unknown and they are being estimated based on the images supplied.

P.S. Justice Type 2 Bayonet, Reference # 247, clearly made in a different style and by a different manufacturer, has a near identical muzzle ring diameter, lock-to-muzzle length and lug slot dimensions.  Without a rifle to test fit, it appears that this bayonet would possibly interchange with the P.S. Justice bayonet.  

Top - PS Justice Bayonet / Bottom - Unknown Collins Bayonet #11