In what anthology was Mushishi serialized that each issue typically has around thirty ongoing stories?
Mushishi:  It was serialized in "Afternoon Seasons Zōkan" from 1999 to 2002, and in "Monthly Afternoon" from December 2002 to August 2008. Monthly Afternoon: Monthly Afternoon (月刊アフタヌーン , Gekkan Afutanūn ) is a Japanese monthly seinen manga anthology published by Kodansha under the "Afternoon" line of magazines. Monthly Afternoon:  Each issue typically has around thirty ongoing stories by various authors and runs about 800 pages.
Monthly Afternoon