Despite a resurgence of progressive rock (Battles, Elysian Fields, Porcupine Tree), few groups worth their effects pedals would cop to the term, mainly because most artists hate being pigeon-holed.

Omar Rodriguez-Lopez, guitarist and producer of The Mars Volta, once pre-empted such discussion by asking rhetorically in a press kit, "How can any innovative, forward-thinking art or music not be progressive?" In other words, the label is not only stifling, it's obvious. But labels are still helpful, and The Mars Volta's first two theme-oriented albums were structured and written too much like Yes albums to escape comparison.

Their new album, "Amputechture," seems to have no overarching narrative, unless the song titles, with their odd juxtapositions and neoligisms (vermicide, "baphomets," "meccamputechture"), represent something bigger than their sum. Still, no major-label group makes incoherence so exciting.

Having developed their mojo in the slightly punkier At the Drive In, Omar and lyricist/vocalist Cedric Bixler-Zavala are not the studied classicos usually associated with '70s prog-rock, but rather manic street screechers whose strict, somewhat pretentious song forms can barely contain their emotional hyperbole. And that's where their exceptional bandmates make a difference. If drummer Blake Fleming evokes any '70s dinosaur, it's Led Zeppelin's John Bonham, and keyboardist Ikie Owens owes more to Booker T. than Rick Wakeman. Some of what The Mars Volta does is pure blues and, like any prog-rock, it sounds a hell of a lot better in concert, where you're less likely to be distracted by things like lyrics. Who understands Martian, anyway?