Several soft-tissue imprints and attachment sites have been discovered on the inside of
 the shell wall and on the apertural side of the septum of various fossil and Recent
 ectocochleate cephalopods.  In addition to the scars of the cephalic retractors, steinkerns
 of the body chambers of bactritoids and some ammonoids from the Moroccan and the
 German Emsian (Early Devonian) display various kinds of striations; some of these
 striations are restricted to thc mural part of the septum, some start at the suture and
 terminate at the anterior limit of the annular elevation.  Several of these features were also
 discovered in specimens of Mesozoic and Recent nautilids.  These structures are here
 interpreted as imprints of muscle fibre bundles of the posterior and especially the septal
 mantle, blood vessels as well as the septal furrow.  Most of these structures were not
 found in ammonoids younger than Middle Devonian.  We suggest that newly formed,
 not yet mineralized (or only slightly), septa were more tightly stayed between the more
 numerous lobes and saddles in more strongly folded septa of more derived ammonoids
 and that the higher tension in these septa did not permit soft-parts to leave imprints
 on the organic preseptum.  It is conceivable that this perrnitted more derived ammonoids
 to replace the chamber liquid faster by gas and consequently, new chambers could be
 used earlier than in other ectocochleate cephalopods, perhaps this process began even
 prior to mineralization.  This would have allowed faster growth rates in derived
 ammonoids.