Wiedmann, J. & Kullmann,J.: Ammonoid sutures in ontogeny and phylogeny.-
The Systematics Association, Special volume 18: 215-255, London 1980.

   Abstract: Because of their complexity ammonoid sutures offer the best method
   of recognizing homologies and, thus, phylogenetic relationships.  The individual
   sutural elements (lobes and saddles) develop during ontogeny in various ways
   which permit large scale ammonoid classification.  In some cases even the lower
   taxa can be classified by means of their sutures.  Many examples show that suture
   phylogeny is related to suture ontogeny, for the genetic principle of additive
   typogenesis is mostly involved and the law of recapitulation therefore applies.
     Sutural lobes have been described by symbols and complete suture lines by
   formulas.  But complete unanimity of symbol terminology has not yet been
   achieved.  Morphographic terminologies (i.e. that of Schmidt, 1921) have been
   abandoned, but there are still two contradictory morphogenetic terminologies
   in existence, i.e. Wedekind's original one (1913) and Ruzhentsev's (1949, 1957).
   Here Wedekind's terminology is favoured because of its priority and its easier
   and more general application to all Paleozoic and Mesozoic ammonites.  This
   terminology is based on the five basic lobes E (external or ventral lobe), L
   (lateral lobe), I (internal or dorsal lobe), A (adventitious lobe) and U (umbilical
   lobe).  Ruzhentsev's terminology is rejected mainly because he used Wedekind's
   prior symbols differently and applied different symbols for homologous elements.
   Also his system is completely inadequate for Mesozoic ammonites.  The basic
   suture types and their implications for ammonoid classification are reviewed.