Columbian Cover Or Postal Stationary

Is this U351? Why it's bigger than what I can find online?

Scott U351 comes in 3 sizes. The Scott catalog is a very simplified envelope listing ignoring sizes.
The literature of the United Postal Stationery Society has the detailed listings.

Thanks!

Wow. What a great cover.
So much going on.
Hooded London Pmk, Advice de Reception markings
The Deal "B" Pmk a new discovery for the Postmark database.
The circle B aux sealing markings never seen before.
The long envelope possibly to suit professional documents.

Rod222, thanks for the comments! I figured that the circle B sealing marks were added by the post office since the date was Oct 12, 1893 and the letter was posted on Oct 11, 1893.

I am a US novice,
I would suggest they were applied by the sender to seal the gummed flap.
You often see senders doing that with stamps.

They are very curious, made for a special, constant service I would guess,
maybe the sender a Law firm etc.
PS The blue "23" matches the franking value.
"56" on the back ?

rod222, they could not be applied by the sender, since this circle B sealing marks have the date on it, which is Oct. 12, 1893 and one day later than the letter was given to the post office. Am I missing something here?

The dated "circle B" markings on the reverse side were applied by registry clerks in New York. These marks are well documented.

Thanks John!

Hyde Park, MA. Oct 11, Cancels on Stamps and the Registry mark #94
NY, NY, Oct 12, registry label, back registry mark and registry B seal,
Liverpool, UK, Oct 20, registry mark.
London, UK, Oct 21, registry mark
Deal, UK, Oct 21, arrival mark

One more question, who added "A.R"?

Thank you.

The AR aux markings are added at the point of registration, a card accompanies the cover to the destination, and returned to the sender after receipt by the addressee.
US may have a differing regime.

My latest AR Card, (Pink, Canada) from a colleague Aug 12th 2012.

To answer your question, who applied the AR handstamp, it was applied in New York city; typically in this period on AR items from the US abroad, AR was applied at the outgoing port, if it hadn't been applied at some earlier point along the route. That particular hs is relatively frequently seen.

Very nice heavy cover. The registration fee was only $.08 of the total postage on this item. As $.05 cents an ounce it took three units of first class postage to send this item. The "B" clerk mark was applied when this item was received at the New York main post office registration room. It was then given the double oval New York mark when it was sent over to the foreign mail department. The crayon scribble is a number assigned to outgoing foreign registered mail when it was packaged in the foreign room to go to the ship.

Thank everyone for the comments!

I agree with the above that the AR (acknowledgement of receipt) was applied in the sending country. I believe an official notice was to be sent to the sender indicating successful delivery of the letter. Yes, they are common.

This cover is on ebay for sale.

https://www.ebay.com/itm/TangStamps...AOSwK~ZbcnJN