Silppery Elm Seeds

I ID this tree as Slippery elm because of the slight notch of the seed sac at the apex.
I found these elm seeds today on my lunch hike. The tree on the right in the photo below is the elm.

I noticed that this was an elm tree but the bark did not resemble an American elm. When I got home and consulted my tree ID books the verdict was Slippery elm.