Let's dispense with the "jam band heroes" tag right at the start. Widely hailed as the improvisational successors of the Grateful Dead and Phish, Umphrey's McGee are nothing of the sort. As the band's detailed liner notes make abundantly clear, their songs are painstakingly composed and meticulously structured, and whatever "improvisation" takes place is far removed from the sometimes aimless noodling of their acid-drenched antecedents. The process is admirably illustrated on Bottom Half, a two-CD compilation of odds and ends that never made the cut on 2006's breakthrough album Safety in Numbers. The B-sides approach generally suggests inferior material. Not this time. Safety in Numbers was originally conceived as a two-CD set -- one electric, the other acoustic. But that approach was abandoned when one of the band's close friends died, and the resulting album took on a much more subdued and somber tone. Bottom Half resurrects the discarded songs, and particularly focuses on the group's more electric and up-tempo side. The first CD features the typical Umphrey's McGee grab bag of genre hopping -- reggae riddims, folk strumming, Southern rock, progressive bluegrass jams (courtesy of special guest Béla Fleck), and jazz fusion excursions that wouldn't have sounded out of place on late-'70s Weather Report or Al di Meola albums. They get Steely Dan funky on "Bright Lights, Big City" and "Iron and Wine," and introspectively mellow on "Home," all the while retaining their own signature sound. It all comes to glorious fruition on "Divisions," a ten-minute Southern rock tour de force that showcases the band's instrumental prowess, and which finds the band's four soloists soaring off into an extended jam that conjures up fond memories of Dickey Betts and Duane Allman guitar duels. Not all of it works. "Memories of Home" can't escape the maudlin clutches of its overly sentimental lyrics. And, in general, the singing is merely serviceable, and provides a few momentary lulls between the dazzling instrumental workouts. But at their best -- and there are many such moments here -- Umphrey's McGee combine the finest aspects of virtuosity and soul. They can really play, and they can play with feeling and fire. The second CD is far more expendable, and will probably only be of interest to hardcore fans. The 28 fragments here -- studio chatter, abortive starts, and demo tracks -- provide an interesting glimpse into the studio habits of the band, but little else. So consider this 50 minutes of first-rate music and 70 minutes of filler. Fortunately, the filler is easily isolated and can be conveniently ignored. What's left offers a convincing case for Umphrey's McGee as an innovative and vital band, restlessly pursuing their decidedly non-improvisational Muse.