Today's riff is from the Styx song "Miss America", which comes from what's probably their most widely known record, The Grand Illusion (1977). In their live show, this was always where James Young would do his bit about how when he was young his parents wouldn't let him play his guitar or his stereo loud, but now he could play his guitar "just as loud as I damn please!" Then he'd do a big guitar solo bit, after which the band would launch into "Miss America" (which he sings lead on). So that was always a big showcase moment for JY (and probably still is, in their current shows). However, the main riff from the song, which is heard in the Intro and the Verses, and which is tabbed here, is played by Tommy Shaw. (In the video footage I linked to below, JY is sometimes playing the riff during the Verses, too, although in a different/lower fretboard position.) 

STYX - "Miss America"      (J. Young)

https://www.angelfire.com/planet/zerofret/annesblog/varriffs.txt

There are several live versions of the song on YouTube. In this one, you can get a pretty clear look at the riff being played in a couple of places:

https://www.youtube.com/watch?v=pWQSdVHKs70