This section is from the book "The American Woman's Cook Book", by Ruth Berolzheimer. Also available from Amazon: The Domestic Arts Edition of the American Woman's Cook Book.
Clean and skin the fish. Insert a sharp knife close to the backbone at the tail end, and cut the flesh from the bone, working toward the head and keeping the knife as close as possible to the bone. Small bones that adhere to the flesh or are embedded in it must be removed with the fingers.
Large fish, such as cod and halibut, are easily boned; in fact, they are usually purchased in slices. Fish with many bones, like shad, can not be boned satisfactorily.
Flounders are often boned, to form fillets, and are served as "fillets of sole." The English sole is seldom imported, and most of the "fillet of sole" that is served in America is made from the flounder, which has a white, delicate flesh similar to the sole.
A fillet is merely a piece of fish without skin and bones. Fillets look better on the serving platter if they are approximately the same size. Rolled fillets are called turbans. They are fastened with wooden toothpicks to keep them in shape during cooking, but the picks are removed before the fish is served.