This bayonet has a typical Collins style short hilt.  The smooth ribbed brass hilt is 119 mm long and has 15 ribs.  The muzzle ring is flush to the hilt flat and the inside diameter is 22.9 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 51 mm long spring are typical Collins construction.  The center of the cross guard has a steel rivet through the blade. 

The lug slot is chamfered around the top edge and there is no guide slot.  The hilt flat is horizontally stamped with a small assembly number, usually two digits.  

 The yataghan blade is 497 mm long and has unstopped fullers.  The left ricasso is stamped  COLLINS & CO / HARTFORD / CONN in three straight lines and the right ricasso is dated 1861.  Sometimes the CONN line is omitted and the date is stamped under HARTFORD.  The CONN line is sometimes stamped upside down and reversed. 

Ed Hull, SABC Journal Volume 4, states that 5000 Model 1841 Rifles were sent from the Watervliet Arsenal to E. Remington & Sons of Ilion, New York, for alterations of only the addition of a bayonet stud and the fitting of the bayonet.  The bayonets were supplied by Collins & Co.  Remington only delivered 3,268 altered rifles, apparently due to the inability to obtain sufficient bayonets from Collins.

Hull identifies the dimensions of this bayonet as follows; the bayonet lug is unique in that it is small at 0.6 inch (15.2 mm) long and 0.38 inch (9.7 mm) wide, without key and has an unusually thin top or cross piece.  The stud-to-muzzle distance is 4.5 inches (114 mm).  Overall lengths vary from 24.5 to 24.875 inches (622 to 632 mm).  The blade lengths vary from 19.875 to 20.25 inches (505 to 514 mm).  The lock spring is 2 inches (51 mm) long and the lug slot is about 1.25 inches (31.8 mm) long.  The flat of the hilt is horizontally stamped with a small assembly number (usually two digits) that was also stamped on the rifles bayonet stud.  The blades are marked on the reverse “COLLINS & CO. / HARTFORD” in two lines, sometimes with “CONN.” stamped in a third line.   Those blades without the “CONN.” marking are sometimes stamped with the date 1861 under the logo.  Others are dated 1861 on the obverse.

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George Moller, American Military Shoulder Arms, claims New York State records show that 2,500 altered rifles with sword bayonets were received from Remington on June 25, 1861.  An additional 768 were received on September 24, 1861 for a total of 3,268.

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The following pictures and information provided by Southpaw Sanctum.

Library of Congress images titled "Washington, D.C. Georgetown ferry-boat carrying wagons, and Aqueduct Bridge beyond, from rocks on Mason's Island".

The New York jacket, the Mississippi rifle, the saber bayonet, and guard duty on the island.  The 45th NY or "5th German Rifles" wore these jackets and were armed with Mississippi rifles and saber bayonets, and they were stationed in the Washington defenses from October 1861 to April 1862.

The soldier on the far right is clearly carrying a sword bayonet on his left hip.

Two of the soldiers standing on the rock and a third soldier on the right with his hand against the tree, appear to have a saber bayonet. 

Up close you can see that the soldier with his hand against the tree has a sword bayonet on his left hip with the hilt flat facing the camera. It appears to be a brass hilted with a short lug slot and no guide bar slot, as would be expected for the NY Alteration.

The two soldiers in the middle and up front provide nice images of the rifles and bayonet scabbards.