Miss Caroline Glyn is fifteen years old. She is the great-granddaughter of the celebrated Elinor Glyn. And with these literary data dutifully recorded, it should hastily be added that she is a prodigiously gifted young novelist who has written about what she knows best remarkably well. Miss Glyn's Don't Knock the Corners Off spans ages nine through fifteen in the life of Antonia Rutherford- a sensitive-but-not-enough-to-make-ya-sick published poetess- in four different educational institutions, none of which succeeds in overcoming her concrete block against the ""simplicities"" of mathematical relationships. This, plus an occasional spur-of-the-moment jaunt to exotic places, with her bohemian parents, is it. Limited? Of course! But few writers have described the terrors of the schoolyard, the calumnies of cafeteria dining, or the anal-orientation of eleven year olds with such frightening accuracy. And to make it even more extraordinary, Miss Glyn has a mature, subtle sense of humor. This fifteen year old, this great-granddaughter of Elinor Glyn, this prodigy--has written a very fine novel.