Your first sight of barefoot Terrance Simien on stage is of a big, Cheshire-cat grin underneath his trademark Fulani hat from Mali. The hat goes on and off; the smile stays put for the next two hours.

Terrance Simien and the Zydeco Experience - a great American band, much better than many better-known bands - came to the friendly Sellersville Theater on Thursday night. No place in Bucks County rocked harder, I guarantee. WXPN, in the midst of Zydeco Crossroads, a 14-month celebration, hosted the evening. And the Sellersville, which runs such a great music lineup, was an ideal setting. Once the band got chugging, most of the crowd quit their seats and took to the floor.

That's what zydeco is: dance-hall music. Simien has had a band since 1981, "when we were teenagers," as he told the audience. He's squeezed the zydeco box ever since. The band offered healthy heaps of both tradition and pop makeovers into zydeco.

They made sure to deliver the hits of the genre: a smokin', spiced-up "Zydeco Boogaloo" (quoting the Jackson Five's "I Want You Back," and during which Simien waved one of the band's Grammy awards, hilariously); "Uncle Buck"; "Ma Chère Catin"; the big hug of trad waltz "Jolie Blonde;" "Dog Hill" ("We from Dog Hill/ Where the pretty women?"); "Iko Iko" (to a Bo Diddley beat); and snatches of "Les Haricots Sont Pas Salé" and "Cornbread." Later, there was the obligatory medley from funk founders the Meters, with "Hey Pocky Way," "People Say," and "Fire on the Bayou."

Some zydeco "purists" chide Simien for going off-campus into pop. But it's silly to be a purist about such a gloriously impure music. From its beginnings, as Louisiana "Saturday night music," zydeco was always self-taught musicians making their favorite tunes their own - urban and rural; black, white, and dirty rice; church and whorehouse; Cajun and Creole; cumbia, soul, and rock and roll; ska, reggae, classic country, marching band, and funk.

So the band regaled the crowd with War's "Cisco Kid," Peter Tosh's "Stop That Train," Bob Marley's "No Woman No Cry," a surprisingly funky version of Stephen Stills' "Love the One You're With," a curveball with Gale Garnett's "We'll Sing in the Sunshine," Dylan's "You Ain't Going Nowhere," and the Band's "The Weight." All zydeco.

What a band: Simien, going from squeezebox to squeezebox, tweaking textures and tones, and singing with his flexible, soulful voice, in homage to Marley, Sam Cooke, Boozoo Chavis, even Louis Armstrong; omnipotent bassist Stan Chambers; keyboard man Danny Williams, Simien's sidekick for decades; guitarist Eric Johanson, he of breathtaking speed, precision, and passion; sax stalwart and frottoirist Josh Lazo, whose solos were among the best received all night; and drummer Oreun Joubert, who played adamantine, rock-steady rhythms in 20 musical languages.

The moving high point was Simien's solo on Cooke's "A Change Is Going to Come," for an audience member fighting cancer: "We want you to fight until there ain't no fight left."

You know it's been a great night when, at the end, your smile muscles are just as tired as your dance muscles.