'... follows the text of the original novel first published in October 1918 issue of "Blue Book Magazine"' - title page verso.
OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
The people that time forgot by Edgar Rice Burroughs. ISBN 0426148320. Published by Tandem in 1975. Publication and catalogue information, links to buy online and reader comments.
