Please look at these pictures first for an idea of my tree.

http://www.duke.edu/~cwcook/trees/ulpa2496.jpg
http://www.glenforrestfirebrigade.or...parvifolia.jpg

I think I have identified a tree that I recently inherited with little
information. It looks very much like these pictures of Ulmus
Parvifolia- the shapes of the leaf and margins are perfect- but my
tree's leaves are slightly lighter colored and less shiny or finished.
Also, the bark is darker and very rough and scaly, but this may be
just because my tree is probably very old (rumored to be 40 or 50
years). My grandmother gave it to me a month ago after my grandfather
(the greater bonsai artist of the two) died, and she said it was a
grapefruit, but it's obvious to me that it's not.

Do you think, despite my described differences, that the tree is a
chinese elm? If so, how should I take care of it in the winter? I live
in New Jersey, and the nights can be below freezing any month from
October-March. Night temperatures in winter stay around 15-25 F and
rarely go below 10 F. We usually get a 1-2 feet of snow each year, but
recently we've had very little.

What other kind of tree might I have?

My tree is about 50 cm tall with a trunk 4 cm in diameter and is
potted in a medium-sized, rectangular ,and shallow bonsai pot. I have
so far seen no signs of flowering, so I'm pretty lost to its
identity.

Thanks for reading and, hopefully, for commenting!