THE SECOND REEL WEST by Bill Pronzini & Martin H. Greenberg (Doubleday: $12.95). All right, Trivial Pursuit buffs: What 1930 musical Western starring Myrna Loy and Frank Fay was inspired by Stewart Edward White's 1907 story "The Two-Gun Man?" Answer: Michael Curtiz's early talkie "Under a Texas Moon." It's one of 10 stories in this second collection of Western tales (the first was last year's "The Reel West") which were adapted for movies ranging from B-pictures like "Black Eagle" (from an O. Henry story) to productions like 'Trooper Hook' (with Barbara Stanwyck doing her stuff as a former Indian captive scorned by whites--a rich, often-mined Hollywood vein). Also appearing in this instructive and entertaining selection: James Warner Bellah's "Command" and "Big Hunt"--the matrix of "She Wore a Yellow Ribbon" (1949), the second part of John Ford's famous "cavalry trilogy"; Dorothy M. Johnson's "A Man Called Horse," a superlative 1949 Collier's story which evolved into a 1970 triumph for actor Richard Harris; and Elmore Leonard's pre-"Glitz" story, "The Captives," which became "The Tall T," a 1957 vehicle for the prototypical Western hero Randolph Scott. One point is clearly reinforced: What moves across the surface of a story gets filmed; what moves downward--such as the roots of a plant, to give taste and substance--is often left behind on the page.