Fans of the acoustic Grateful Dead, as well as of New Riders of the Purple Sage and Jerry Garcia’s side project, Old & In the Way, should pay attention to this hard-driving New England string band. Hot Day at the Zoo plays what it calls “zoograss’’ - a mix of folk, rock, and progressive bluegrass charged with a jam-band flavor that makes this live set (recorded at the Waterhole in Saranac Lake, N.Y.) a bracing treat. The group excels on a touchstone cover of “Midnight Moonlight’’ (the Peter Rowan song from Old & In the Way’s self-titled disc in 1973), but the bulk of the CD is original tracks from multitalented Hot Day tunesmiths Mike Dion (whose sweeping “Morning Light’’ makes a nice companion piece to “Midnight Moonlight’’) and Jon Cumming, whose gentle “Long Way Home’’ is a tasteful change-of-pace from the string-band flash. At times the music is rich in testosterone (as in the pot-smoking anthem “Old Mill’’), and it is less elegant than New Riders of the Purple Sage, but those are about the only quibbles. Otherwise, these guys accelerate with a euphoric banjo/mandolin interplay, enhanced by the inspired stand-up bass of Jed “Beat’’ Rosen and occasional, roaring harp fills from the ever-energetic Dion. The crowd in Saranac Lake goes crazy - and so might you if you give this a listen. The band headlines the Lizard Lounge this Friday and Saturday. (Out tomorrow)