Penelope Fitzgerald won the 1979 Booker Prize for this slim, delicate novel, which illustrates the lives of a motley assortment of houseboat-dwellers on the Thames River in the 1960's. Fitzgerald, one of the great prose stylists of the 20th century, is gentle, but incisive with her characterizations. As a former houseboat-dweller herself, she knew of what she wrote.  (GBR329, $12.95)