Sorry can't help you with the different shapes but found this reall great desciption of what-not's online.
hope this is of some help to you.
WHAT-NOT, a piece of furniture, derived from the French ÃƒÂ©tagÃƒÂ¨re, which was exceedingly popular in England in the first three-quarters of the 19th century. It usually consists of slender uprights or pillars, supporting a series of shelves for holding china, ornaments or trifles of any kindÃ¢â‚¬â€hence the allusive name. In its English form, although a convenient drawing-room receptacle, it was rarely beautiful. The early mahogany examples are, however, sometimes graceful in their simplicity.