Hi Janet,
I don't really have an opinion one way or the other about which species of Tilia it is. Just going off the pictures, Tilia x euchlora is as good a match as any other species of Tilia, better than most.
But, Tilia americana is a wildly variable species, so much so that it has been confounding botanists for decades. Just for entertainment, look at all of the species of Tilia that were described at one time or another, but are now lumped into just three varieties of Tilia americana:
http://www.itis.gov/servlet/Si...
http://www.itis.gov/servlet/Si...
http://www.itis.gov/servlet/Si...
If you ask a forester how to tell Tilia americana from Tilia cordata the answer will be something along the lines of 'americana has big leaves with oblique bases and cordata has small leaves with cordate bases'. However, leaf size and shape is all over the place with Tilia americana (
http://www.hort.uconn.edu/plan...) even on the same tree. They vary quite a bit with Tilia cordata (
http://www.hort.uconn.edu/plan...) as well. I would guess the same is true for Tilia x euchlora. Just as an example, its leaves are described as being cordate on the UConn Plant Database site, but the accompanying pictures show leaves with oblique bases!
http://www.hort.uconn.edu/plan...
I hope this long and rambling post isn't taken as a disagreement over the ID of the tree. I just question whether there is really enough information in the pictures to say with any certainty which species of Tilia it is.
Pictures of the flowers would help (Tilia americana *usually* has whitish flowers while T. cordata and T x euchlora *usually* have yellowish flowers), but it's obviously too late for that this year
