Cross-reference,
Heading-reference,
First-word-reference,
Series-entry.
Specific entry,
E. g., registering “The art of painting” under Painting, or a description of the cactus under Cactus. Putting them under Fine arts and Botany would be class-entry. “Specific entry,” by the way, has nothing to do with “species.”
Subject,
It is worth noting that subjects are of two sorts: (1) the individual, as Goethe, Shakespeare, England, the Middle Ages, the ship Alexandra, the dog Tray, the French Revolution, all of which are concrete; and (2) general, as Man, History, Horse, Philosophy, which may be either concrete or abstract. Every general subject is a class more or less extensive. (See note on Class.) Some mistakes have also arisen from not noting that certain words, Poetry, Fiction, Drama, etc., are subject-headings for the books written about Poetry, Fiction, etc., and form-headings for poems, novels, plays, etc.