From INTRODUCTION, p.130:
     We have made an extensive survey of septal necks in Paleozoic and
  Mesozoic Ammonoidea based on well-preserved specimens from many re-
  gions throughout the world (see Appendix).  Our data base includes material
  from 107 species belonging to 27 superfamilies distributed among eight
  suborders. This chapter synthesizes our observations on these septal necks
  and includes a discussion of their evolution and morphogenesis.