What Kind Of Cancel On "Special Delivery" From NYC Dated 1904

I found on a letter dated 1904, Special Delivery, domestic mail to NYC a postmark, that I can not classify.
This is the front:




And here the back with the mentioned postmark:




This marked postmark is my problem. What kind is it? Does it have something to do with the special delivery? A postmark from the delivering mailman? Exist this only from NYC? Is there any publication, philatelic society or something, that research these postmarks? Exist a website about it? In the old publication "speedy" about these stamps I found nothing about it.

So many question because a small postmark. I hope some will be answered.
Regards
Juergen

A New York City station receiving cancel. Note your cancel is the last applied chronologically. See this thread for several illustrations of similar cancels:

http://goscf.com/t/71937

Many thanks John Becker. Also for the link. This old threat about the same question I had completely forgotten. Sorry!!
Juergen