The _classified_ catalogue--the best accessible example of which is the catalogue of the Carnegie Library of Pittsburgh (1895-1902, supplements, 1902-06 and 1907-11), while good English examples are issued by The Patent Office, Newcastle-upon-Tyne, Islington (selected catalogue), Bolton and Walthamstow--is gradually ousting the dictionary catalogue from the favour of librarians. In this form books are arranged in the order of the classification, in the perfect form in the strict order of it, and under each specific heading the books can be arranged alphabetically or (preferably) in chronological or inverse-chronological order, or in the order which places the best book first. Such a catalogue shows the whole “family” literature of every subject in a logical progression, and is therefore much more valuable to the student than other forms. It must, however, be equipped with author and subject indexes to make it usable by ordinary readers who have not grasped the scheme of classification; such indexes are usually placed at the end of the catalogue, or class if the catalogue is issued in class lists, and the catalogue is prefaced with an outline of the scheme. The _alphabetical-classed_ catalogue is one in which the books are arranged under specific subjects and the subject headings are arranged in alphabetical order. Excellent examples of the method are the Library Association _Index to Periodicals_ and (with briefer entries) the London Library _Subject Index_, and the British Museum _Subject Index_. As the last two examples show, this form is usually provided as an index to be used in conjunction with a separate author catalogue, but complete, individual catalogues have been produced in this form. Its advantages are those accruing to the alphabet, rapid reference and easy recognition; its disadvantages are the inevitable separations of allied topics.