Robert Crumb enters the ’70s “On the Crest of a Wave” with the sixth volume in Fantagraphics Books’ reprint series.This includes a couple of genuine rarities,as well as all of Crumb’s work from Big Ass #1, Zap #4 (including the legendary, much-busted “Joe Blow”), the remarkably offensiveSnatch #3 and Jiz #1,Despair —classics all.