Who knew that library school could be so funny?
Here is a rule from the fat tome of AACR2 (Anglo-American Cataloging Rules 2nd edition):

21.26 Spirit Communications
21.26A. Enter a communication presented as having been received from a spirit under the heading for the spirit (see 22.14). Make an added entry under the heading for the medium or other person recording the communication.

Food for the million, or, Thoughts from beyond the borders of the material / by Theodore Parker ; through the hand of Sarah A. Ramsdell
Main entry under the heading for the spirit of Parker
Added entry under the heading for Ramsdell

Apparently, Mark Twain has written stuff from beyond the grave. I believe that there are books or pamphlets in some library somewhere that have been attributed to: Twain, Mark (Spirit)