Complex sentence: Heitmüller was a prominent member of the "Religionsgeschichtliche Schule" (History of Religions School), and with Wilhelm Bousset (1865-1920) was editor of journal "Theologische Rundschau".
Split into simpler sentences: Heitmüller was a prominent member of the "Religionsgeschichtliche Schule" (History of Religions School). With Wilhelm Bousset (1865-1920), he was editor of the journal "Theologische Rundschau".