Here's what Alan has to say about them....
NATIONAL LINE RAINBOS
Among Peltier's most popular marbles are the National Line Rainbos, which were produced as early as the late 1920s and up to the late 1930s. All National Line Rainbos will exhibit two seams, which differentiates them from the earlier Miller swirls. Most have an opaque base, though some are semi-opaque or translucent. The design will consist of "ribbons" of opaque to transparent color. There will be one or more colors represented on the ribbons, and usually there will be four or six ribbons present. Rarely, the ribbons will have aventurine glass in them, usually in black ribbons but also present on extremely rare occasions in blue or red ribbons. Aventurine is a type of glass with finely ground particles of copper (golden), chromic oxide (green), or ferric oxide (red), which causes it to sparkle under illumination, especially direct sunlight.
Dragon (light green with red ribbons)
Flaming Dragon (light green with red and yellow ribbons---usually the colors are blended to create a more orange effect)