TABLE OF CONTENTS. 



Page. 



Part 1. Triad syBtems on 15 elements whose group is of order higher than unity 5_ 



By H. S. White. 



Part 2. Trains for triad systems on 15 elements whose group is of order higher than unity 27 



By Louise D. Cummings. 



Part 3. Groupless triad systems on 15 elements 69 



By H. S. White and Louise D. Cummings. 

 Part 4. Structure as defined by interlacLngs, heads, and semiheads; a complete census of triad systems in 15 



elements - 73 



By F. N. Cole. 



Pajit 5. Sequences and indices for all groupless triad systems on 15 elements 81 



By Louise D. Cummings. 



3 



