This work lists 20,000 genealogies that were not in the Library of Congress when the Bibliography and First Supplement were published. It includes additions and corrections to those volumes as well as an index of 10,000 secondary names. Code letters designate the libraries in which all these items may be found. Altogether the holdings of 24 major libraries are listed, though this figure may actually be said to represent 45 libraries, since the Allen County Library of Fort Wayne, Indiana, possesses photo and microform copies of genealogies from 21 additional libraries.