For his 17th novel, Larry McMurtry, the Pulitzer Prize-winning author of Lonesome Dove and The Last Picture Show, has seen fit to take on a collaborator, Diana Ossana, whose jacket-flap biography announces with an understandable note of defensiveness that she has ''been writing ever since she learned to read.'' Far be it from a lowly reviewer to plumb the mysteries of the creative mind and heart that prompted this unlikely teaming. What matters is what's on the page, and on those terms, Pretty Boy Floyd (Simon & Schuster, $24), a spirited fictional biography of the Depression-era bank robber, is pretty good McMurtry. Or McMurtry/Ossana. Or whatever.
Floyd finds the author (you know which one I mean) back in the American folktale mode that has served him so well in 19th-century Westerns. But he's richly aware that by the 1930s, the renegade spirit of the frontier was harder to locate, and so it had to be manufactured. That may be why populist outlaws like Charles Arthur Floyd, an Oklahoma bumpkin portrayed here as the sweetest guy ever to become Public Enemy No. 1, became cultural icons.
Pretty Boy Floyd, its authors tell us, began life as a screenplay, and like many a crime-spree movie, it's brisk and strongly crafted scene by scene, but its also episodic and a bit impersonal. The characters are immediate and vivid, thanks largely to the hilariously plainspoken vernacular that comes out of their mouths, but they're also broadly drawn and sometimes cartoony. Which isn't to say that Floyd lacks emotional ballast; a single scene can swoop deftly from light picaresque into heartbreak and out again. It's tempting to ascribe the novel's most economical effects to McMurtry, who reports that he wrote ''a skeletal five pages'' a day that were plumped up to 10 by his collaborator, and to blame Ossana for such faintly embarrassing ornamentations as ''Part of him wanted to remember; part of him needed to forget.'' But instead of grading them separately, let's just average their marks. B