Hey, Ralph!
Unfortunately, I can't read "Sumer Is Icumen In" without the tune running through my head, and I can't make yours cooperate with the music that Anon's (obviously) and Ezra Pound's fit so well.
There's a YouTube version of a nice performance
here. Note that the Pes 1 and Pes 2 ("pes" is Latin for "foot") parts chase each other in their own little mini-round throughout--playing footsie?--beneath the main round. And here are links to the
original and
modernized sheet music, if you want to sing along.)