Marcellliesz's lectures delivered on October 1957 -January 1958 at the Uni- versity of Maryland, College Park, have been previously published only infor- mally as a manuscript entitled CLIFFORD NUMBERS AND SPINORS (Chap- ters I - IV). As the title says, the lecture notes consist of four Chapters I, II, III and IV. However, in the preface of the lecture notes lliesz refers to Chapters V and VI which he could not finish. Chapter VI is mentioned on pages...