Studio Astrology Series
Publisher: Viking Press
Related Series: Studio Handbooks
A bit of a stretch, in that none of the 12 titles are numbered in a traditional way. I'm including this series because you can make a loose series number out of the calendar dates that correspond to the astrological sign and their ISBNs are in sequence (see the Aug. 31, 1970, PW ad).
Ad, PW, June 15, 1970, at 6:
Ad, PW, Aug. 31, 1970, at 182 (indicating release date for all 12 titles is Oct. 13, 1970, and listing all titles with SBNs).